This is a test configuration based on an excellent BGP tutorial by Router Gods. http://www.routergods.com
(Router Gods are really excellent. Thanks for the template, guys!)
Step 1: Configure addresses as shown and then configure internal routing between R3 and R7, using OSPF. All routers have loopbacks of x.x.x.x/24, matching router number. (eg R3 – 3.3.3.3)
router ospf 1
network 0.0.0.0 0.0.0.0 area 0
All routers from R3 to R7 are to be considered an internal network. R1 and R2 are the external network. R3 is therefore on the edge.
Step 2 Configure fa0/0 on R3 as a passive interface. You don’t want it to form neighbours with anyone else as it is on the edge.
router ospf 1
passive-interface fa0/0
Step 3 Configure a default gateway on R3 as the edge router: ip route 0.0.0.0 0.0.0.0 10.10.13.2
Step 4 Make all traffic move to R3 as default using default-information originate command.
R3(config)#router ospf 1
R3(config-router)#default-information originate always
Step 5 Set up a peer from R3 to R1. R3 ASN is 100. R1 ASN 666
R3(config)#router bgp 100
R3(config-router)#neighbor 10.10.13.2 remote-as 666
R1(config)#router bgp 666
R1(config-router)#neighbor 10.10.13.1 remote-as 100
R1(config-router)#exit
R1(config)#exit
R1#sh ip bgp summary
BGP router identifier 1.1.1.1, local AS number 666
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
10.10.13.1 4 100 2 2 0 0 0 00:00:01 0
Useful debug: debug ip tcp transactions
Test: Shut down and restarted one of the interfaces. Debug output below, as link is re-established.
*Mar 2 21:51:17.576: Released port 179 in Transport Port Agent for TCP IP type 1 delay 240000
*Mar 2 21:51:17.580: TCB 0x66215C14 destroyed
R1#
*Mar 2 21:51:30.412: TCB66216524 created
*Mar 2 21:51:30.416: Reserved port 179 in Transport Port Agent for TCP IP type 1
*Mar 2 21:51:30.416: TCP0: state was LISTEN -> SYNRCVD [179 -> 10.10.13.1(41764)]
*Mar 2 21:51:30.416: TCP: tcb 66216524 connection to 10.10.13.1:41764, peer MSS 1460, MSS is 516
*Mar 2 21:51:30.420: TCP: sending SYN, seq 3653985059, ack 3463377124
*Mar 2 21:51:30.420: TCP0: Connection to 10.10.13.1:41764, advertising MSS 1460
*Mar 2 21:51:30.456: TCP0: state was SYNRCVD -> ESTAB [179 -> 10.10.13.1(41764)]
*Mar 2 21:51:30.460: TCB66214BC8 callback, connection queue = 1
*Mar 2 21:51:30.460: TCB66214BC8 accepting 66216524 from 10.10.13.1.41764
*Mar 2 21:51:30.472: TCB66214BC8 setting property TCP_IN_TTL (29) 651003A0
*Mar 2 21:51:30.472: TCB66214BC8 setting property TCP_OUT_TTL (30) 651003A0
*Mar 2 21:51:30.472: TCB66216524 setting property TCP_OUT_TTL (30) 66467F2A
*Mar 2 21:51:30.540: %BGP-5-ADJCHANGE: neighbor 10.10.13.1 Up
Step 5. Peer with loopback addresses if desired.
R1(config)#router bgp 666
R1(config-router)#no neighbor 10.10.13.1 remote-as 100
R1(config-router)#neighbor 3.3.3.3 remote-as 100
R1(config-router)#exit
(You will also need to create static routes between loopbacks. BGP will generally not work with default routes. You need to configure a static route there and back.)
Because TTL on BGP is normally 1, you need to configure multihop to get to the loopback, on both sides.
R1(config-router)#neighbor 3.3.3.3 ebgp-multihop 3
R1(config-router)#exit
Step 6. Redistribute routes. As an example, redistribute the OSPF routes on R3 – advertise routes into BGP. (Pretend that the 10 networks in AS100 are internet routable)
R3(config)#router bgp 100
R3(config-router)#redistribute ospf 1
R3(config-router)#exit
If you look at R1 you can now see new routes injected in to BGP:
R1#sh ip bgp
BGP table version is 14, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete
Network Next Hop Metric LocPrf Weight Path
*> 3.3.3.0/24 3.3.3.3 0 0 100 ?
*> 4.4.4.4/32 3.3.3.3 11 0 100 ?
*> 5.5.5.5/32 3.3.3.3 21 0 100 ?
*> 6.6.6.6/32 3.3.3.3 22 0 100 ?
*> 7.7.7.7/32 3.3.3.3 32 0 100 ?
r> 10.10.13.0/24 3.3.3.3 0 0 100 ?
*> 10.10.34.0/24 3.3.3.3 0 0 100 ?
*> 10.10.35.0/24 3.3.3.3 0 0 100 ?
*> 10.10.45.0/24 3.3.3.3 20 0 100 ?
*> 10.10.67.0/24 3.3.3.3 31 0 100 ?
*> 192.168.35.0 3.3.3.3 30 0 100 ?
*> 200.1.1.1/32 3.3.3.3 32 0 100 ?
Note that the r route is not injected into the table because there is already a connected route.
Step 7. You can configure networks in BGP manually as well. (Put a prefix into BGP)
R1(config-router)#network 66.66.66.0 mask 255.255.255.0
R1(config-router)#exit
R1(config)#
However, this will not appear in the BGP routing table (sh ip bgp) unless it has a route to that host already.)
Step 8 Configure security
R3(config)#router bgp 100
R3(config-router)#neighbor 1.1.1.1 password cisco
R3(config-router)#exit
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