While going through some BGP examples in Routing TCP/IP Volume II, I came across an issue where RIB failures continue to pop up in the show commands. To illustrate see the following topology I recreated from the book (pg 175, fig 3-6 on Routing TCP/IP II book)

sh ip bgp produces the following output with the “r>” indicating that there is a RIB failure in router Vail.

sh ip bgp rib-failure provides a clue as to what caused the RIB failure

Further troubleshooting shows why

Telluride is advertising prefixes 192.168.1.200/30, 192.168.50.0, and 192.168.75.0 via IBGP towards Vail. Vail, however, is also learning these same routes via OSPF through Aspen. As shown in the sh ip route output for one of the routes above, an OSPF advertisement has an AD of 110, whereas an IBGP advertisement has an AD of 200. Even though the routes are in Vail’s BGP table, the OSPF route is installed in the routing table because of lower administrative distance. BGP then throws a fit because he has the routes in his table and the router ignored him.

This is normal operation for BGP. In fact, even though Vail does not use the route via BGP it is not suppressed or thrown out. If you check the ip routing table in Taos, you’ll see that BGP is sending these same routes from Vail. So at least BGP is happy there

I’m starting to contemplate taking the CCIP track. I’ve been having a lot of fun with MPLS and BGP lately that I have  this compelling urge to go all the way with the IP track. The only thing that really holds me back is QoS. LOL! For some weird reason, QoS can’t seem to sit well with me. I don’t think it’s way more complicated than either MPLS or BGP, in terms of understanding the concepts. It’s just that it doesn’t seem to arouse interest in me. But then again, frame relay used to suck for me, but now we’re coo.

So CCIP or not? If I do, it would push back my goal of getting the CCIE R&S. On the upside, I’ll probably know BGP well enough to get it out of the way in my CCIE studies. MPLS doesn’t go much in depth in CCIE R&S but taking the CCIP MPLS exam should give me that much more command of the technology.

We shall see where it leads me. For now, to more MPLS fun…

So I’m speaking with one of the engineers that will probably be the point person that will implement MPLS for us. I noticed in my studies that nearly all of the configurations required to implement MPLS happen in the Provider space. All these PEs, Ps, LSRs all reside in the service provider from which I have no access to. This particular engineer pretty much confirmed that, yes, the implementation will be “seamless and almost transparent” to the IT staff. To those who are unfamiliar with sales-speak, seamless and transparent basically means it will be installed without adverse affect to the current system (seamless) and almost no change in our network equipments’ configuration (transparent). Well booo.. For once I actually want to get into some trouble mis-configuring things . I was joking around with the engineer that maybe they can hire me just for that project and let me do the configurations. I’ll even let my company pay the work I’m doing for them.

Anyway, it’s all good. I’m learning more and more about MPLS and I like it. Currently I’m building a small dynamips lab based on the sample scenarios from the book I’m reading. FYI, I’m reading MPLS Fundamentals by Luc De Ghein should thou wondereth. So far I’m enjoying the book. First time reading the MPLS VPN section got my brain all tied and twisted. But the second time around, concepts are beginning to come together more coherently. I’m also enjoying the fact that I get to lab BGP in the context of applying it to a different technology. Other than labbing BGP, as a technology by itself, and the occasional redistribution between different IGPs, I’m now able to see how it is used in MPLS.

So, bummer.. but, s’guuuuudd!!

I’ve been cleaning up some ACLs on our PIX at work. I’ve manage to trim this:

access-list acl_outside extended permit tcp any host PublicIP eq 3200
access-list acl_outside extended permit tcp any host PublicIP eq 3201
access-list acl_outside extended permit tcp any host PublicIP eq 3202
access-list acl_outside extended permit tcp any host PublicIP eq 3203
access-list acl_outside extended permit tcp any host PublicIP eq 3204
access-list acl_outside extended permit tcp any host PublicIP eq 3205
access-list acl_outside extended permit tcp any host PublicIP eq 3206
access-list acl_outside extended permit tcp any host PublicIP eq 3207
access-list acl_outside extended permit tcp any host PublicIP eq 3208
access-list acl_outside extended permit tcp any host PublicIP eq 3209
access-list acl_outside extended permit tcp any host PublicIP eq 3210
access-list acl_outside extended permit tcp any host PublicIP eq 3211
access-list acl_outside extended permit tcp any host PublicIP eq 3212
access-list acl_outside extended permit tcp any host PublicIP eq 3213
access-list acl_outside extended permit tcp any host PublicIP eq 3214
access-list acl_outside extended permit tcp any host PublicIP eq 3215
access-list acl_outside extended permit tcp any host PublicIP eq 3216
access-list acl_outside extended permit tcp any host PublicIP eq 3217
access-list acl_outside extended permit tcp any host PublicIP eq 3218
access-list acl_outside extended permit tcp any host PublicIP eq 3219
access-list acl_outside extended permit tcp any host PublicIP eq 3220
access-list acl_outside extended permit tcp any host PublicIP eq 3221
access-list acl_outside extended permit tcp any host PublicIP eq 3222
access-list acl_outside extended permit tcp any host PublicIP eq 3223
access-list acl_outside extended permit tcp any host PublicIP eq 3224
access-list acl_outside extended permit tcp any host PublicIP eq 3225
access-list acl_outside extended permit tcp any host PublicIP eq 3226
access-list acl_outside extended permit tcp any host PublicIP eq 3227
access-list acl_outside extended permit tcp any host PublicIP eq 3228
access-list acl_outside extended permit tcp any host PublicIP eq 3229
access-list acl_outside extended permit tcp any host PublicIP eq 3230
access-list acl_outside extended permit tcp any host PublicIP eq 3231
access-list acl_outside extended permit tcp any host PublicIP eq 3232
access-list acl_outside extended permit tcp any host PublicIP eq 3233
access-list acl_outside extended permit tcp any host PublicIP eq 3234
access-list acl_outside extended permit tcp any host PublicIP eq 3235
access-list acl_outside extended permit tcp any host PublicIP eq 3236
access-list acl_outside extended permit tcp any host PublicIP eq 3237
access-list acl_outside extended permit tcp any host PublicIP eq 3238
access-list acl_outside extended permit tcp any host PublicIP eq 3239
access-list acl_outside extended permit tcp any host PublicIP eq 3240
access-list acl_outside extended permit tcp any host PublicIP eq 3241
access-list acl_outside extended permit tcp any host PublicIP eq 3242
access-list acl_outside extended permit tcp any host PublicIP eq 3243
access-list acl_outside extended permit tcp any host PublicIP eq 3244
access-list acl_outside extended permit tcp any host PublicIP eq 3245
access-list acl_outside extended permit tcp any host PublicIP eq 3246
access-list acl_outside extended permit tcp any host PublicIP eq 3247
access-list acl_outside extended permit tcp any host PublicIP eq 3248
access-list acl_outside extended permit tcp any host PublicIP eq 3249
access-list acl_outside extended permit tcp any host PublicIP eq 3250
access-list acl_outside extended permit tcp any host PublicIP eq 3251
access-list acl_outside extended permit tcp any host PublicIP eq 3252
access-list acl_outside extended permit tcp any host PublicIP eq 3253
access-list acl_outside extended permit tcp any host PublicIP eq 3254
access-list acl_outside extended permit tcp any host PublicIP eq 3255
access-list acl_outside extended permit tcp any host PublicIP eq 3256
access-list acl_outside extended permit tcp any host PublicIP eq 3257
access-list acl_outside extended permit tcp any host PublicIP eq 3258
access-list acl_outside extended permit tcp any host PublicIP eq 3259
access-list acl_outside extended permit tcp any host PublicIP eq 3260
access-list acl_outside extended permit tcp any host PublicIP eq 3261
access-list acl_outside extended permit tcp any host PublicIP eq 3262
access-list acl_outside extended permit tcp any host PublicIP eq 3263
access-list acl_outside extended permit tcp any host PublicIP eq 3264
access-list acl_outside extended permit tcp any host PublicIP eq 3265
access-list acl_outside extended permit tcp any host PublicIP eq 3266
access-list acl_outside extended permit tcp any host PublicIP eq 3267
access-list acl_outside extended permit tcp any host PublicIP eq 3268
access-list acl_outside extended permit tcp any host PublicIP eq 3269
access-list acl_outside extended permit tcp any host PublicIP eq 3270
access-list acl_outside extended permit tcp any host PublicIP eq 3271
access-list acl_outside extended permit tcp any host PublicIP eq 3272
access-list acl_outside extended permit tcp any host PublicIP eq 3273
access-list acl_outside extended permit tcp any host PublicIP eq 3274
access-list acl_outside extended permit tcp any host PublicIP eq 3275
access-list acl_outside extended permit tcp any host PublicIP eq 3276
access-list acl_outside extended permit tcp any host PublicIP eq 3277
access-list acl_outside extended permit tcp any host PublicIP eq 3278
access-list acl_outside extended permit tcp any host PublicIP eq 3279
access-list acl_outside extended permit tcp any host PublicIP eq 3280
access-list acl_outside extended permit tcp any host PublicIP eq 3281
access-list acl_outside extended permit tcp any host PublicIP eq 3282
access-list acl_outside extended permit tcp any host PublicIP eq 3283
access-list acl_outside extended permit tcp any host PublicIP eq 3284
access-list acl_outside extended permit tcp any host PublicIP eq 3285
access-list acl_outside extended permit tcp any host PublicIP eq 3286
access-list acl_outside extended permit tcp any host PublicIP eq 3287
access-list acl_outside extended permit tcp any host PublicIP eq 3288
access-list acl_outside extended permit tcp any host PublicIP eq 3289
access-list acl_outside extended permit tcp any host PublicIP eq 3290
access-list acl_outside extended permit tcp any host PublicIP eq 3291
access-list acl_outside extended permit tcp any host PublicIP eq 3292
access-list acl_outside extended permit tcp any host PublicIP eq 3293
access-list acl_outside extended permit tcp any host PublicIP eq 3294
access-list acl_outside extended permit tcp any host PublicIP eq 3295
access-list acl_outside extended permit tcp any host PublicIP eq 3296
access-list acl_outside extended permit tcp any host PublicIP eq 3297
access-list acl_outside extended permit tcp any host PublicIP eq 3298

To this:

access-list acl_outside extended permit tcp any host 108.13.137.83 range 3200 3299

Anybody have any idea how to shrink the following?

static (inside,outside) tcp PublicIP 3200 10.100.194.28 3200 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3201 10.100.194.28 3201 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3202 10.100.194.28 3202 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3203 10.100.194.28 3203 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3204 10.100.194.28 3204 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3205 10.100.194.28 3205 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3206 10.100.194.28 3206 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3207 10.100.194.28 3207 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3208 10.100.194.28 3208 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3209 10.100.194.28 3209 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3210 10.100.194.28 3210 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3211 10.100.194.28 3211 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3212 10.100.194.28 3212 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3213 10.100.194.28 3213 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3214 10.100.194.28 3214 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3215 10.100.194.28 3215 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3216 10.100.194.28 3216 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3217 10.100.194.28 3217 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3218 10.100.194.28 3218 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3219 10.100.194.28 3219 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3220 10.100.194.28 3220 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3221 10.100.194.28 3221 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3222 10.100.194.28 3222 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3223 10.100.194.28 3223 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3224 10.100.194.28 3224 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3225 10.100.194.28 3225 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3226 10.100.194.28 3226 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3227 10.100.194.28 3227 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3228 10.100.194.28 3228 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3229 10.100.194.28 3229 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3230 10.100.194.28 3230 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3231 10.100.194.28 3231 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3232 10.100.194.28 3232 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3233 10.100.194.28 3233 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3234 10.100.194.28 3234 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3235 10.100.194.28 3235 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3236 10.100.194.28 3236 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3237 10.100.194.28 3237 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3238 10.100.194.28 3238 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3239 10.100.194.28 3239 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3240 10.100.194.28 3240 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3241 10.100.194.28 3241 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3242 10.100.194.28 3242 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3243 10.100.194.28 3243 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3244 10.100.194.28 3244 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3245 10.100.194.28 3245 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3246 10.100.194.28 3246 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3247 10.100.194.28 3247 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3248 10.100.194.28 3248 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3249 10.100.194.28 3249 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3250 10.100.194.28 3250 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3251 10.100.194.28 3251 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3252 10.100.194.28 3252 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3253 10.100.194.28 3253 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3254 10.100.194.28 3254 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3255 10.100.194.28 3255 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3256 10.100.194.28 3256 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3257 10.100.194.28 3257 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3258 10.100.194.28 3258 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3259 10.100.194.28 3259 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3260 10.100.194.28 3260 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3261 10.100.194.28 3261 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3262 10.100.194.28 3262 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3263 10.100.194.28 3263 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3264 10.100.194.28 3264 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3265 10.100.194.28 3265 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3266 10.100.194.28 3266 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3267 10.100.194.28 3267 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3268 10.100.194.28 3268 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3269 10.100.194.28 3269 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3270 10.100.194.28 3270 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3271 10.100.194.28 3271 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3272 10.100.194.28 3272 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3273 10.100.194.28 3273 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3274 10.100.194.28 3274 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3275 10.100.194.28 3275 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3276 10.100.194.28 3276 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3277 10.100.194.28 3277 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3278 10.100.194.28 3278 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3279 10.100.194.28 3279 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3280 10.100.194.28 3280 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3281 10.100.194.28 3281 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3282 10.100.194.28 3282 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3283 10.100.194.28 3283 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3284 10.100.194.28 3284 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3285 10.100.194.28 3285 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3286 10.100.194.28 3286 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3287 10.100.194.28 3287 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3288 10.100.194.28 3288 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3289 10.100.194.28 3289 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3290 10.100.194.28 3290 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3291 10.100.194.28 3291 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3292 10.100.194.28 3292 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3293 10.100.194.28 3293 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3294 10.100.194.28 3294 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3295 10.100.194.28 3295 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3296 10.100.194.28 3296 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3297 10.100.194.28 3297 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3298 10.100.194.28 3298 netmask 255.255.255.255
static (inside,outside) tcp PublicIP 3299 10.100.194.28 3299 netmask 255.255.255.255

Ok, Ok, I know I said in a previous post that I will be going away from my usual bullet-style blog posts. But I just can’t see any better way to take notes than to do it the way I’ve been doing it for the last couple of years. So here are some notes I’ve compiled over the last few days on MPLS.

MPLS

• Stands for Multi-Protocol Label Switching
• Uses a new way for routers to forward packets. Instead of the traditional way of  forwarding packets based on destination IP address, MPLS routers forward packets using MPLS labels.
  • Label Switching indicates that the packets are no longer IPv4 packets, IPv6 packets, or even Layer 2 frames when switched. They are instead labeled.
• MPLS allows forwarding decisions based on other factors, such as:
  • Traffic Engineering
  • QoS requirements
  • Privacy requirements for multiple customers connected to the same MPLS network (MPLS VPN)

MPLS Header and Label

• The MPLS header is a 4-byte (32-bit) field, located immediately before the IP header

• The header is also often times referred to as a shim header.
• Most will simply refer to the MPLS header as the MPLS label, but in fact the label is actually a 20-bit field in the MPLS header.
  • The label identifies the portion of a label switched path (LSP). LSP will be discussed later.
  • The label value can be between 0 and 1,048,575 (or 2^20 – 1)
• The MPLS EXP bits is a 3-bit field used for QoS marking. Historically it was called Experimental because the actual used for it was then undetermined.
• The bottom-of-stack (S) field (1-bit) is a flag, which when set to 1, means that this is the label immediately preceding the IP header. (see label stacking)
• Time-to-Live (TTL) is an 8-bit field used for the same purpose as the IP header’s TTL field.

Label Stacking

• Label stacking is the encapsulation of an MPLS packet inside another MPLS packet. In other words, an MPLS header is added “on top of” an existing MPLS header; hence “stacking”.
• This is done so that one MPLS LSP can tunnel inside another LSP.
• The first label in the stack is called the top label.
• The last label is called the bottom label.

•  The BoS bits for all labels is 0 except the very bottom, which has a value on 1. A value of 1 means that this label is the bottom label and is immediately followed by the IP header.

Encapsulation of Labeled Packet

• The label stack sits in front of the Layer 3 packet, before the header of the transported protocol, but after the Layer 2 header.

• The MPLS label stack is often called the shim header because of the placement of the packet in the frame.
• The Layer 2 encapsulation of the link can almost be any encapsulation that Cisco supports. For example:
  • PPP
  • High-Level Data Link Control (HDLC)
  • Ethernet
• The transported protocol could be anything:
  • IPv4
  • IPv6
  • Frame Relay
  • PPP
  • HDLC
  • ATM
  • Ethernet

Label Switch Router

• A Label Switch Router (LSR) is a router that supports MPLS. It is capable of understanding MPLS labels and or receiving and transmitting a labeled packet on data link.
• Three kinds of LSRs:
  • Ingress (edge) LSR – receives unlabeled packet from customers equipment. It inserts a label in front of the packet and send it on a data link.
  • Egress (edge) LSR – receives labeled packets, removes the labels, and send them onto the data link towards the customer’s equipment.
  • Intermediate LSR – receives labeled packets, perform an operation on them, switches the packet, and send the packet on the correct data link.
• LSRs can do three types of operation:
  • Pop – removes labels.
  • Push – adds the label onto the received packet
  • Swap – the top label of the label stack is replaced with a new label and the packet is switched on the outgoing data link.
• Imposing LSR – an LSR that pushes labels onto a packet that was not labeled yet. Done by the ingress LSR.
• DisposingLSR – removes all labels form the packet. Done by the egress LSR.

Label Switched Path

• It is the path through which a packet takes in the MPLS network (or part of it).
• It is a sequence of LSRs that switch a labeled packet through an MPLS network.
• The LSP is unidirectional. That means a path to go back requires a complete separate LSP.

Forwarding Equivalance Class

• An FEC is a set of packets that a sintgle router forwards:
  • To the same next hop
  • Out the same interface
  • With the same forwarding treatment
• All packets belonging to the same FEC have the same label.

Comparison

• In a regular IP forwarding process, each time a packet reaches a router, a lookup is performed on the IP destination, the packet’s FEC (that is, the next-hop, outgoing interface, and forwarding treatment) is determined. Using the gathered information the packet is forwarded to the next router. When the packet arrives to that router, this whole process is repeated.
  • Essentially, the packet’s FEC is determined hop-by-hop at every router that it reaches on its way to the destination.
• In an MPLS LSP, when a packet arrives at the first LSR, the FEC is determined once and is not repeated until that packet reaches the end of the LSP – the egress LSR. The intermediate LSRs  does not determine a new FEC, as compared to the regular IP forwarding process.

Label Distribution Protocol

• For the label distribution in an MPLS LSP to work, each intermediate LSR needs to figure out which outgoing label the incoming label should be swapped.
• LDP is the method of choice among the majority of MPLS vendors to distribute labels for IGP prefixes.
• LDP is the mechanism that tells the routers which labels to use when forwarding a packet.
• For every IGP IP prefix in an LSR’s IP routing table, a local binding is created. A label is binded to an IPv4 prefix. The LSR then distributes this binding to all its LDP neighbors. Once receved by other neighbors, these local bindings become remote bindings. These remote and local bindings are stored in a table called Label Information Base (LIB). The LIB contains all lables known to the LSR
• LDP uses a Hello feature to discover LDP neighbors and to determine to what IP address the enusing TCP connection should be made.
  • Hellos use multicast address 224.0.0.2, using UDP port number 646 for LDP
  • The Hellos list each LSR’s LDP ID (LID), which consists of a 32-bit dotted-decimal number and a 2-byte label space number (this number has a value of 0 for frame-based MPLS).
• After discovering neighbors via an LDP Hello message, LDP neighbors form a TCP connection to each neighbor, again using port 646 (for TDP, port 711 is used).
• The unicast address used to form the TCP connections between neighbors must be reachable according to the IP routing table. These addresses can be either the neighbor’s advertised transport address or the address in the LID.
• Cisco IOS chooses the IP address in the LPD ID in the following priority (similar to OSPF):
  • Manually configured address
  • Highest IP address of a loopback
  • Highest ID of a non-loopback interface

Label Forwarding Instance Base

• While the LIB contains all labels know to the LSR, the LFIB (and the FIB) contains labels only for the currenlty used best LSP segment.
• LFIB is the table used to forward labeled packets.
• It is populated with the incoming label and outgoing labels for the LSPs
• The incoming label is the label from the local binding ont the particular LSR.
• The outgoing label is the label from the remote binding chosen by the LSR from all possible remote bindings.

In the following diagrams, observe how LDP advertises bindings betweent the LSRs for the IPv4 prefix 10.0.0.0/8 and how packet switching works when a packet destined to the 10.0.0.0/8 prefix enters the ingress LSR.

• In the part of the illustration, each LSR allocates one label per IPv4 prefix. This prefix and its assocated label is the local binding
• An LSR chooses the remote binding received from the downstread LSR, which is the next hop in the routing table for the 10.0.0.0 prefix. 
• The label from the local bindings server as the incoming label and the label from the one remote binding chosen via the routing table serves as the outgoing label.
• The bottom of the figure shows a packet entering the Ingress LSR destined to 10.0.0.0/8.
• There, a label 129 is imposed on the packet and switched toward the next LSR. The second LSR swaps the incomgin label 129 with 17 and forwards to the next LSR. The incoming label 17 is again swapped with the outgoing  label 33.

If I’m inspired, the next post will focus more on the Data Plane and Control Plane of the MPLS forwarding process. And if I’m really brave, I’ll re-read and blog-note the section on MPLS VPN.

References

1. Understanding MPLS Label Stacking – Jeff Doyle – NetworkWorld
2. MPLS FAQ For Beginners
3. Understanding the Role of FECs in MPLS – Jeff Doyle – NetworkWorld

This entry is not an authoritative guide. These are merely notes and rehash of the primary text materials and resources that I use. For a thorough guide of the MPLS concepts, consider purchasing MPLS Fundamentals byLuc De Ghein and the MPLS section of CCIE Routing and Switching Certification Guide (4th Edition) by Wendell Odom; as well as following the links on the reference section of this entry.

Recently my interest in Carrier-type technology has been re-invigorated since we decided to order and install MPLS in all our offices. I’ve always been intrigued by MPLS. Several years ago I did a little bit of studying about what MPLS is about and what advantages it offers over traditional IP or Ethernet transport. Although I learned about the gist of MPLS, I didn’t really go in depth to really understand the technology. Mainly because, first, our company did not deploy or make use of the technology, and secondly I was also heavily invested in my CCNP studies.

But now that I and management have been talking to different  vendors and carriers about installing MPLS, I have been reading a lot more about the technology in a little bit more depth. It also happens that I am beginning my preparations to take the CCIE R&S written lab as well – and a little portion of MPLS is in the blue print for the exam. So I think this could get a little fun for me.

I have been on a hiatus from blogging since passing my BCMSN (I passed on July 30, 2010), and I have been very liberal in my study schedule. I haven’t had a set or planned pattern to follow and as a result my progress has been very ineffective. I would watch a technology video here and there, take a topic and read/study  it here and there, but nothing really learned or stuck in my long term memory.

So as I always do before the start of the New Year, I’m re-affriming my resolution to pass more certifications. Last year I only accomplished 1/3 of my professional-oriented New Year’s resolution; which I consider a failure. So for the coming year, I’ll be doing the same. I haven’t laid out exactly what they would be but it’ll definitely include finally getting the CCNP or at the very least passing the R&S written.

In the last several weeks I have started reviewing my BCMSN stuff. In fact, I’m re-doing my BCMSN study regimen that I set out for myself when I started studying for it. I have just finished going through and labbing fundamental STP/RSTP concepts. Hopefully I can get through the materials faster this time. I have forgotten many of the BSCI concepts so I definitely need to spend more time on that. But as I’m finding out, even though I have more recently passed BCMSN, relative to BSCI, I’m still finding things on switchnig topics that seemed like new concepts for me, even though I know I’ve studied them before. I think it’s just a matter of repetition until these topics become imprinted in my memories.   

More than likely, I will probably abandon my old outline-format blog style. At least for the time being. A lot of the things that I go through in my review are concepts that I’ve blogged about before. In fact, I’ve been using my blog as a review material when going back through old subjects. And I’m glad I spent a lot of times blogging my notes. But moving forward,  a lot of my blog entries will be updates of what I’m doing. I may blog some lab practices from time to time to help me hammer in some concepts.

Anyway, Merry Christmas and Happy New Year to all my friends out there.

I took my BCMSN exam on Saturday July 24, 2010. As you can tell from the title of the post, I failed. I’m a bit disheartened by the outcome. Although I felt nervous, like I always do, coming into the exam, I was confident I could pass it. I was not over-confident. I just felt that I had enough knowledge to get through.

Here’s how I did:

Implement VLANs: 100%
Spanning Tree: 90%
Implement Inter-VLAN routing: 80%
Implement gateway redundancy technologies: 75%
Describe and configure wireless client access: 40%
Describe and configure security features in a switchted network: 25%
Configure support for voice: 25%

Passing score: 804
My score: 731

Notice how the pattern in the scores go from highest to lowest in exactly the same order that Cisco lays out the exam topic. In a way it’s a telling pattern as to how my learning path progressed. In all the study resources I read, the texts were arranged pretty much in the same order as the BCMSN blueprint is layed out. Consequently, I spent a whole lot more time on the topics higher up on the list than I did on topics further down the list. And the scores reflect that. However that is not to say I didn’t feel as prepared on the topics I scored lowest on as I did on the topics I scored the highest. I believe it’s also in the way the exam itself was layed out.

The number one reason I failed the test is time management. No matter how much I read about how you need to manage your time, this always seems to be what gets me. Just to give you an idea of my horrendous management of time:

• Out of nearly 60 exam questions, I still had about 15 left by the time the exam expired.
• There were 2 sim questions on which I spent nearly 20 minutes working on. It didn’t help that these sim questions came in within the first 15 exam questions.
• In each of the sim questions, I spent almost 5 minutes just lingering around checking and double checking that my configurations were correct.

The only positive thing about spending that much time in the configuration sections is that I”m pretty sure I got them both correct or pretty close to being correct. The two sim questions had a lot to do with setting up VLANs, checking spanning tree configuration, and manipulating spanning tree behaviour. And as you can see on the breakdown of the scores, I scored a 100% and 90% on each topic, respectively.

The fact that I spent almost half of my allotted time on the sims and the fact that I still had about 15 questions remaining tells me that had I managed my time better and finished the exam, I might have had enough points to pass. I don’t believe that my scores on wireless and voice is telling of how much I know or don’t know about the topics. Actually, without having finished the exam, I have no way of knowing if I really know enough about those topics or if I should focus more on those topics before my next attempt. My gut tells me to focus more on getting faster on configuration.

Here are some of my thoughts on why I took so long on the sims:

• I need to get better at understanding what the question is asking and get down to the requirements of the configuration. I’m always caught off guard by questions that include background scenarios that don’t necessarily pertain to what the problem is asking me to solve.
• I tend to linger on one part of the solution over and over trying to make sure that I configured it correctly even after I’ve correctly verified through show commands that the outcome being asked for has been fulfilled. For example, I had a problem where I needed to make a configuration change so that one trunk interface is the preferred path over another. When I was finally able to accomplish the task, I verified it over and over and over again that it was correct.. and there were 3 more tasks waiting to be completed. 
• I really need to memorize commands in addition to understanding it. A huge part of the problem with the configuration was that I knew what I needed to do but I forget what the exact commands are. Was it spanning-tree vlan root primary or spanning-tree root primary vlan? Was it an interface configuration or a global configuration?  

This is my first Cisco exam fail. This is probably not going to be the last – although, ideally, it should be. I always read on many people’s blogs and in forums those comments who have failed an exam, and they always say how passable the exam is and how fair the questions were. And I always thought to myself, how can people fail and exam and afterwards think that it is totally fair and passabel. Well.. ironically, I find myself in the same situation with the same sentiments about the exam. I thought it was totally fair and totally passable.

I would write more about my thoughts on my experience but writing about passing an exam is more fun than writing about failure. So I’m getting back on the horse and ride again. Next test is scheduled July 30th.

I’m on a horse! Heeyaa!!!!

I know I said I wasn’t going to blog my notes just yet until after I finished the exam. But it’s a funny thing.. studying is. I used to complain that I need to get rid of my distractions so I can study better. I have had a lot of things in my mind the past few days. But last night, after watching the Lakers beat the Celtics I got to study a little bit and took some notes. The weird thing about it is that, ironically, studying became a huge distraction from my own thoughts.  The game was a huge distraction too. I just needed a little distraction. And studying was the ticket.

I read halfway through the wireless section of the BCMSN Exam Guide. I went back to re-read and took some notes on key points and definitions until I got too tired and lazy to continue.  Nothing new or revealing on the following notes. They can be helpful for review later. It’s also not complete or comprehensive.

• 802.11 uses CSMA/CA vs. 802.3 which uses CSMA/CD – Avoidance vs. Detection.
• Distributed Coordination Function (DCF) – wireless stations wait a certain duration value before transmitting frames.
• Service Set – group of wireless devices
• Service Set Identifier (SSID) – A string included in every frame set; the devices must share a common SSID.
• Independent Basic Service Set (IBSS) – ad hoc network; where 2 or more wireless clients directly communicate with each other with no other means of network connectivity.
• Basic Service Set (BSS) – one access point
  • Match SSID
  • Compatible wireless data rate
  • Authentication

• Extended Service Set (ESS) – More than one APs placed at different geographic locations.
• Access Points can act:
  • As connection point for wireless clients, or
  • Act as a bridge to form a single wireless bridge from one LAN to another over a long distance – AP-to-AP or line of sight links.
• An AP is in charge of mapping a VLAN to an SSID.
  • When an AP uses multiple SSIDs, it is in effect trunking VLANs over the air to end users.
  • Example: VLAN 10 mapped to SSID “Marketing” and VLAN 20 mapped to SSID “Engineering”
• Cell – an AP’s coverage area.
• Reducing the transmit power on an AP reduces the cell size -  causing only clients close by to associate with it. That means less clients hogging the bandwidth. The others can associate with another AP closer to them.
• Microcells – when cell sizes are reduced
• Picocells – cell sizes are minimized even more
• Frequency – oscillating signal based around a constant.
  • Radio Frequency (RF)
• Band – broad range of frequencies used for similar funcations
  • AM Radio band consists of the frequency range 550 MHz through 1720 MHz.
  • Wireless can be in 2.4 GHz band or 5GHz band.
• Carrier Signal – the signal transmitted by a wireless station.
  • No audio, video, or data is present in the carrier itself.
• Modulate/Demodulate – in order to transmit information, the transmitter must modulate the carrier signal by inserting or encoding the information in a unique fashion. Receiving devices demodulates the signal.
• Channel – a fixed frequency, that varies within a certain range, which a transmitter and receiver expects the carrier to appear on

I’ve been offline far too long. That doesn’t mean I haven’t been working though. I’ve been getting ready for the BCMSN exam, trying to beat the July 31st deadline before it expires. I feel kind of ready but I’m not 100 percent. I’m in the stage where I think I can pass the exam if I took it now but also too cautious not to  be too confident. And when I feel that way, then I’m not ready.

Studying has been very hard. I have not had the motivation I once had. Last night I was reviewing some of my blog notes and humbly, I felt these notes were pretty damn good. I ask myself why I stopped doing these notes. And I have to believe that others also find my notes pretty helpful as well based on a small sampling of positive comments I was getting.

Anyway, I came to a resolve last night that after I’ve taken the BCMSN exam, I’ll resume back with my old note-taking style and start blogging my notes again. Why after the exam? Taking these notes is incredibly time consuming. It literally takes at least 4-6 hours per blog entry. That’s taking into account one full reading of the subject matter, re-reading the important points, taking a summary, researching Cisco docs to verify that what I’ve written is in fact correct (and even then I still make factual mistakes). If I were to start these note-blogs again, I will not be ready to take the exam before the expiration date.

Anyway, based on the still-decent-daily-hit-count I get on my blog, thanks for visiting and continuing to support this blog through your comments, suggestions, and readership.