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10/21/10 12:43 PM
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Mitch Baker
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Any of you helpful fellers able to lay down some plain english BGP implementation/configuration discussion here? Im sick of reading material that reads like stereo instructions.

I understand that BGP uses whats already in the routing table based off any IGP's that are running. What im having a hard time with is how to get routes from an IBGP AS to be advertised via EBGP to a remote AS.

anyone?

anyone?

big slacker?
10/21/10 2:11 PM
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big_slacker
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Lemme demo this so it makes sense. I've got three routers, R2, R3 and R6. They are all connected to a frame relay network with a common subnet 24.234.100.0/24.

R2 and R3 are IBGP peers in AS 65000

R2 only is an EBGP peer with R6 who is in AS 65006

R2 and R3 have network statements for some of their connected networks, we'll look at one for network 24.234.121.0/24. Here are the BGP configs for each:

R2#sho run | sec bgp
router bgp 65000
no synchronization
bgp log-neighbor-changes
network 24.234.22.0 mask 255.255.255.0
network 24.234.100.0 mask 255.255.255.0
network 24.234.252.0 mask 255.255.255.0
neighbor 24.234.100.3 remote-as 65000
neighbor 24.234.100.6 remote-as 65006
no auto-summary

R3#sho run | sec bgp
router bgp 65000
no synchronization
bgp log-neighbor-changes
network 24.234.100.0 mask 255.255.255.0
network 24.234.121.0 mask 255.255.255.0
neighbor 24.234.100.2 remote-as 65000
no auto-summary

R6#sho run | sec bgp
router bgp 65006
no synchronization
bgp log-neighbor-changes
network 24.234.111.0 mask 255.255.255.0
network 24.234.222.0 mask 255.255.255.0
neighbor 24.234.100.2 remote-as 65000
no auto-summary

They're all neighbored up fine, and simply because there is a network statement in R3's BGP config for 24.234.121.0, it will sho up in the routing table of both R2 and R6. This happens even though R3 is not directly neighbored with R6. Nothing else is needed to advertise networks other than that network statement.

R2#sho ip route 24.234.121.0
B 24.234.121.0 [200/0] via 24.234.100.3, 00:10:08

R6#sho ip route
B 24.234.121.0 [20/0] via 24.234.100.3, 00:07:28
10/21/10 2:14 PM
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big_slacker
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Now, I suspect your question may be (correct me if I'm wrong) that what I showed works fine for BGP, but how do I get routes learned from an IGP into BGP so that they'll be advertised? The answer is redistribution, I'll fire up EIGRP on R2 and learn some routes from a neighbor.

R2(config)#router eigrp 1
R2(config-router)#no auto-summary
R2(config-router)#network 24.234.22.0 0.0.0.255
Oct 21 18:31:09.614: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 24.234.22.100 (FastEthernet0/0.22) is up: new adjacency

R2#sho ip route (snip)
D EX 172.16.99.0/24
[170/28416] via 24.234.22.100, 00:00:47, FastEthernet0/0.22

Ok, so we've got that EIGRP learned route to 172.16.99.0/24. Lets redistribute EIGRP into BGP and see if that shows up on R6.

R2(config)#router bgp 65000
R2(config-router)#redistribute eigrp 1

R6#sho ip route (snip)
B 172.16.99.0 [20/28416] via 24.234.100.2, 00:00:21

There you have it. Network statements within BGP to advertise networks either to IBGP or EBGP peers. Redistribution to get an IGP into BGP.
10/21/10 3:28 PM
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Mitch Baker
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GOD DAMN IT YOU ARE THE FUCKING MAN!
10/21/10 5:38 PM
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big_slacker
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Edited: 10/21/10 5:37 PM
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Basic BGP is easy, people are scared of it because its the internet. And nobody wants to fuck up the internet. :D
10/21/10 6:00 PM
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Mitch Baker
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lol

im in the NOC at an ISP

the only people here who really know bgp are the architect and his cronie.

today i made him explain all of the details about our upstream provider and who we have transit through and stuff.

im going to build the network you mentioned above today or tomorrow.
thanks again frendo!!!
10/26/10 11:05 AM
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mauler
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Mitch,

I started my networking career in an ISP, and its my belief that ISP are the best place to learn BGP (especially with all your peers). I work for a media site now, and REAL BGP is done at the ISP Level IMO. Redistributing other routing protocols like ospf, or eigrp into bgp is rather trivial once you know it.

As long as you have enables on your peer routers. Read the running config, in combination with your sh commands.
This way you will be able to learn how to use regexp, route-maps, as-path (^, $, _ ) their meanings meaning.

Good luck with everything.
10/26/10 2:46 PM
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Mitch Baker
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I have literally only come across the regexp shit once in my studies. It is part of the BSCI Cisco Academy material I found online.

When I saw the ^ and the $'s I started to get a little worried.

I have been studying so much for so long that I feel like I've actually gotten worse somehow. I still plan on taking ROUTE by 1/1/11 though.

Supposedly there is a new BGP Video Mentor series coming out by Cisco Press at the end of this month. I am building the network BigSlacker gave but I still need more reference material.

This test is rough. By the time I have covered all the material I feel as though I have started forgetting the first shit I started with.

ACK!!!
10/26/10 2:51 PM
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Mitch Baker
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yo Slack!

Do you by any chance have the full configs for that lab?

If not, no worries!
10/26/10 9:00 PM
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big_slacker
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PM me an e-mail and I'll send it to you.
10/26/10 9:10 PM
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big_slacker
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Mauler is correct BTW, real BGP is done by ISPs. When a job description asks for BGP they generally mean can you peer up if the ISP gives you an IP and ASN.

ISPs are going to do vrf's, RD/RTs, route maps to tweak metrics, next hop and all the fun stuff. I do highly recommend learning the ins and outs anyway because its pretty fascinating, regardless of whether you think you'll use it or not on OTJ.
10/28/10 5:54 PM
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Mitch Baker
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PM sent
10/28/10 5:59 PM
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Irregular John
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big_slacker - Basic BGP is easy, people are scared of it because its the internet. And nobody wants to fuck up the internet. :D

Haha, a buddy of mine works as a senior engineer for Level 3. One day during a routine maintenance he ran "no router bgp".

Hilarity ensued. They even got that printed on a shirt for him.
10/28/10 7:05 PM
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Mitch Baker
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Irregular John - 
big_slacker - Basic BGP is easy, people are scared of it because its the internet. And nobody wants to fuck up the internet. :D

Haha, a buddy of mine works as a senior engineer for Level 3. One day during a routine maintenance he ran "no router bgp".

Hilarity ensued. They even got that printed on a shirt for him.




I'm a big fan of "debug all"
12/5/10 9:34 PM
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Mitch Baker
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ttt
12/6/10 8:35 AM
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big_slacker
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Its been my experience that many of the folks that teach CCNA have only worked on small networks and then the classroom so they've no concept of capacity or resources issues.

Not their fault really, because even 2800/2900 series routers in a small/medium network as so capable they'll often never see much load.
12/6/10 5:26 PM
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Mitch Baker
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u all is not really a problem if you are...

A) local to the router

and B) have your config written

GO NUTS I SAY!!!!

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