More Trainsignal

I made it through all four of the trainsignal OSPF videos from Trainsignal. I will say that I am completely impressed by Chris Bryant’s teaching and have been very happy with the products so far. My only issue has been the brief explanation he gave on stub areas/NSSA. I found his explanations of NSSA, specifically, to be a little confusing. I’m familiar with how they work and have set them up in lab scenarios, so I’m not concerned for myself… I just thought a little more time could have been spent on them. Maybe he’ll get to it a little more in depth with redistribution.

I don’t have much going on today. We’re doing some work at a remote site this evening, so we’ve been pretty relaxed today. I decided to start the BGP videos, since that’s one of the areas I’m lacking. Just as a side note… I really need to get a better PC to load dynamips on. I have a great rack at home, but I can’t afford to leave it running 24/7 (power consumption). It’d be nice to be able to load a few 2600’s on my work PC, but dynamips keeps crashing. I have a P4 1.8 with 1.5 gigs of RAM, and everytime I load a pair of 2621XM’s (for IOS 12.4), the damned server crashes.

Anyway… Some of the key points from the first hour of the BGP video were:
1. Two classes of attributes: well known and optional. (He didn’t go any further than this just yet.)
2. BGP uses TCP port 179 for communication and uses keep alives to maintain connection.
3. Full tables are exchanged during the relationship establishment. Following that, updates are only sent when a change occurs.
4. Cisco recommends that eBGP peers are directly connected, though there wasn’t any mention of whether or not this is REQUIRED. iBGP peers to not need to be directly connected.
5. BGP states:
a. idle
b. connect
c. active
d. opensent
e. openconfirm
f. established (this is what you want to see when running show ip bgp neighbor and show ip bgp summary)

ebgp_multihop.jpg
A Sample configuration for the above:

R1#conf t
R1(config)#router bgp 100
R1(config-router)#neighbor 172.12.123.3 remote-as 200

R3#conf t
R3(config)#router bgp 200
R3(config-router)#neighbor 172.12.123.1 remote-as 100

If we wanted to use loopback interfaces for additional stability (this would come into play for iBGP with multiple paths to each host, and eBGP with two direct links between peers), we would use the following:
R1#conf t
R1(config)#router bgp 100
R1(config-router)#neighbor 3.3.3.3 remote-as 200
R1(config-router)#neighbor 3.3.3.3 ebgp-multihop 2
(we use the multihop command because we are not peering with the IP address directly connected to us.  The 2 is the number of hops we need to traverse)
R1(config-router)#neighbor 3.3.3.3 update-source lo0 (this is telling the local router to use lo0 as the source of all bgp traffic.  No matter what interface we use to communicate with 3.3.3.3, we will use that Lo as the source IP. )

One of the gotchas was to make sure that we had routes to the loopback interfaces on each side. Since we’re not running an IGP between the two, we opted to use static routes. In Chris’s video, R1 and R3 were connected through a frame switch. He used the interface option in his static route, and the adjacency never came up. When he changed the static route to use the next hop, it came up.

Chris also went through some basic network information in BGP.
First and foremost, when you advertise a network in BGP, you must use the EXACT mask that you have setup or that exists in your routing table. EX:
R1#conf t
R1(config)#interface lo1
R1(config-if)#ip addr 11.11.11.11 255.255.255.255

would require the following network statement in BGP:
R1(config-router)#network 11.11.11.11 mask 255.255.255.255

whereas
R1#conf t
R1(config)#interface lo1
R1(config-if)#ip addr 11.11.11.11 255.255.255.0

would require this statement:
R1(config-router)#network 11.11.11.0 mask 255.255.255.0
The command show ip bgp on the local router will tell you if the route is being advertised to it’s peers.

I want to make it through the rest of the BGP sections and IPv6 before Saturday so I can spend the day working on these labs. My wife will be at another baby shower, and is taking the rugrat with her. I’m determined to get this exam done by Friday of next week.

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