Teaching is the best form of learning, so I will be using this
blog and other venues to post my thoughts on topics related to the CCIE R &
S lab exam to help me, and hopefully others, through the long journey of
studying and learning to prepare for the lab exam. So to begin I'm starting
with a core technology BGP and from the beginning.
I hope to create a series of real labs that teach specific topics
for the lab based on the version 5 blueprint. So to begin I've started with a
basic concept in BGP, establishing neighbors.
Concepts tested
- Establishing iBGP Peerings
- Establishing EBGP Peerings
- BGP Update Source Modification
- Multihop EBGP Peerings
- Neighbor Disable-Connected-Check
- Authenticating BGP Peerings
Complete the following tasks:
- Establish an iBGP peering between R2 and R3 using their loopback 0 interfaces
- Advertise R2 and R3's loopback 10-13 into BGP
- Establish an eBGP peering between R1 and R2 and R1 and R3. Ensure that even if the serial1/0 link on R2 goes down the peering between R1 and R2 stays up. You cannot modify the TTL settings (no ebgp-multihop command) for the peering between R1 and R2 to accomplish this but you can between R1 and R3.
- Establish an eBGP secure peering between R3 and R4 using the password CISCO1
Topology used
 |
| Lab 1 |
Solution Below:
1.
Establish an iBGP peering
between R2 and R3 using their loopback 0 interfaces
R2(config)#router bgp 200
R2(config-router)#neighbor 3.3.3.3 remote-as 200
R2(config-router)#neighbor 3.3.3.3 update-source loopback 0
R3(config)#router bgp 200
R3(config-router)#neighbor 2.2.2.2 remote-as 200
R3(config-router)#neighbor 2.2.2.2 update-source loopback 0
Verify:
R2#sh ip bgp summary
<snip>
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ
Up/Down State/PfxRcd
3.3.3.3 4 200 4 4 1 0 0
00:00:14 0
R3#sh ip bgp summary
<snip>
Neighbor V AS MsgRcvd MsgSent TblVer
InQ OutQ Up/Down State/PfxRcd
2.2.2.2 4 200 11 8 9 0 0
00:03:44 0
2.
Advertise R2 and R3's
loopback 10-13 into BGP
R2(config)#router bgp 200
R2(config-router)#network 172.16.0.0 mask 255.255.255.0
R2(config-router)#network 172.16.1.0 mask 255.255.255.0
R2(config-router)#network 172.16.2.0 mask 255.255.255.0
R2(config-router)#network 172.16.3.0 mask 255.255.255.0
R3(config)#router bgp 200
R3(config-router)#network 172.16.4.0 mask 255.255.255.0
R3(config-router)#network 172.16.5.0 mask 255.255.255.0
R3(config-router)#network 172.16.6.0 mask 255.255.255.0
R3(config-router)#network 172.16.7.0 mask 255.255.255.0
Verify:
R2#sh ip bgp
<snip>
Network Next Hop Metric LocPrf Weight Path
*> 172.16.0.0/24
0.0.0.0 0 32768 i
*> 172.16.1.0/24
0.0.0.0 0 32768 i
*> 172.16.2.0/24
0.0.0.0 0 32768 i
*> 172.16.3.0/24 0.0.0.0 0 32768 I
R3#sh ip bgp
<snip>
Network Next Hop Metric LocPrf Weight Path
*>i172.16.0.0/24
2.2.2.2 0 100
0 i
*>i172.16.1.0/24
2.2.2.2 0 100
0 i
*>i172.16.2.0/24
2.2.2.2 0 100
0 i
*>i172.16.3.0/24
2.2.2.2 0 100
0 i
3.
Establish an eBGP peering
between R1 and R2 and R1 and R3. Ensure that even if the serial1/0 link on R2
goes down the peering between R1 and R2 stays up. You cannot
modify the TTL settings (no ebgp-multihop command) for the peering between R1
and R2 to accomplish this but you can between R1 and R3.
R2(config-router)#neighbor 1.1.1.1 remote-as 100
R2(config-router)#neighbor 1.1.1.1 update-source loopback 0
R2(config-router)#neighbor 1.1.1.1 disable-connected-check
R1(config-router)#neighbor 2.2.2.2 remote-as 200
R1(config-router)#neighbor 2.2.2.2 update-source loopback 0
R1(config-router)#neighbor 2.2.2.2 disable-connected-check
The disabled-connected-check command disables the code in IOS BGP
that verifies if two eBGP peers are directly connected. Technically this check
is what prevents eBGP peering with loopback connections between directly
connected hosts not the TTL.
Reference: Cisco command reference link
Verify R1 to R2:
R2#sh ip bgp sum
<snip>
Neighbor V AS
MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
1.1.1.1 4 100 24 26 9 0 0
00:18:46 0
R1#sh ip bgp sum
<snip>
Neighbor V AS MsgRcvd MsgSent TblVer
InQ OutQ Up/Down State/PfxRcd
2.2.2.2 4 200 37 34 41 0
0 00:28:29 8
Verify R1 to R3:
R1#sh ip bgp sum
<snip>
Neighbor V AS
MsgRcvd MsgSent TblVer
InQ OutQ Up/Down State/PfxRcd
3.3.3.3 4 200 8 7 41 0
0 00:02:37 8
R3#sh ip bgp sum
<snip>
Neighbor V AS MsgRcvd MsgSent TblVer
InQ OutQ Up/Down State/PfxRcd
1.1.1.1 4 100 10 12 9 0 0
00:05:35 0
4.
Establish an eBGP secure
peering between R3 and R4 using the password CISCO1
R3(config)#router bgp 200
R3(config-router)#neighbor 4.4.4.4 remote-as 200
R3(config-router)#neighbor 4.4.4.4 update-source loopback 0
R3(config-router)#neighbor 4.4.4.4 ebgp-multihop 255
R3(config-router)#neighbor 4.4.4.4 password CISCO1
R4:
R4(config)#router bgp 400
R4(config-router)#neighbor 3.3.3.3 remote-as 200
R4(config-router)#neighbor 3.3.3.3 update-source loopback 0
R4(config-router)#neighbor 3.3.3.3 ebgp-multihop 255
R4(config-router)#neighbor 3.3.3.3 password CISCO1
Verify:
R3#sh ip bgp sum
<snip>
Neighbor V AS MsgRcvd MsgSent TblVer
InQ OutQ Up/Down State/PfxRcd
4.4.4.4 4 400 7 8 9 0 0
00:03:36 0
R4#sh ip bgp sum
<snip>
Neighbor V
AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
3.3.3.3 4 200 8
6 9 0
0 00:03:03 8
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