Summer was in full swing, and it was over 105 degrees Fahrenheit outside. Bob was told it was a “dry heat”, but he thought “so is my oven”. Needless to say, Bob was glad to be in the data center, where the temperature and humidity controls kept it very cold. He had been asked to setup up a basic route-map with BGP, and here is the diagram he worked from.
The goal, was to modify BGP, so that all traffic going towards the 1.1.1.0 network (which is sourced from AS1), traveling either from or through AS23, would only use the 13.0.0.0/24 segment (between R3 and R1), and not use the 10.0.0.0/24 segment (between R2 and R1) as a transit path.
Bob reviewed some of the BGP topics he had recently learned. Here is the list he made of possibilities:
R1 could pre-pend to the AS path for advertisements of the 1.1.1.0/24 prefix when it is sent to R2 from R1. This way, AS23 would see a better path through R3 rather than R2. He tried this using the following on R1:
Bob decided to try another approach, and instead of R1 trying to make AS23 think the path on 10.0.0.0 was worse, perhaps he would tell R3 to make the path on 13.0.0.0 look better. He considered weight, but then realized that would only work for R3, and not every other device in AS23. So Bob decided to use local-preference. On R3, he tried using local-preference, to specify that when a BGP update came in from R1 for 1.1.1.0, R3 would set the local-preference to 250 for that prefix, in hopes that this would allow traffic destined for 1.1.1.0 go exclusively through the 13.0.0.0 segment between R3 and R1. Unfortunately, even with this change, Bob noticed that traffic destined to 1.1.1.0 from our through AS23 still crossed on the link between R2 and R1.
Below are the configurations for R1, R2 and R3 along with the relevant show commands.
Can you assist Bob? What can he do? What did he do wrong, if anything?
Post your ideas and comments below!
R1:
The goal, was to modify BGP, so that all traffic going towards the 1.1.1.0 network (which is sourced from AS1), traveling either from or through AS23, would only use the 13.0.0.0/24 segment (between R3 and R1), and not use the 10.0.0.0/24 segment (between R2 and R1) as a transit path.
Bob reviewed some of the BGP topics he had recently learned. Here is the list he made of possibilities:
R1 could pre-pend to the AS path for advertisements of the 1.1.1.0/24 prefix when it is sent to R2 from R1. This way, AS23 would see a better path through R3 rather than R2. He tried this using the following on R1:
ip prefix-list JUST-1.1.1.0 seq 5 permit 1.1.1.0/24Bob cleared the BGP session, just to be sure. Unfortunately, some traffic destined to 1.1.1.0 was still flowing over the 10.0.0.0 network between R2 and R1.
route-map PRE-PEND permit 10
match ip address prefix-list JUST-1.1.1.0
set as-path prepend 1
route-map PRE-PEND permit 20
router bgp 1
neighbor 10.0.0.2 route-map PRE-PEND out
Bob decided to try another approach, and instead of R1 trying to make AS23 think the path on 10.0.0.0 was worse, perhaps he would tell R3 to make the path on 13.0.0.0 look better. He considered weight, but then realized that would only work for R3, and not every other device in AS23. So Bob decided to use local-preference. On R3, he tried using local-preference, to specify that when a BGP update came in from R1 for 1.1.1.0, R3 would set the local-preference to 250 for that prefix, in hopes that this would allow traffic destined for 1.1.1.0 go exclusively through the 13.0.0.0 segment between R3 and R1. Unfortunately, even with this change, Bob noticed that traffic destined to 1.1.1.0 from our through AS23 still crossed on the link between R2 and R1.
Below are the configurations for R1, R2 and R3 along with the relevant show commands.
Can you assist Bob? What can he do? What did he do wrong, if anything?
Post your ideas and comments below!
R1:
version 12.4R2:
hostname R1
interface Loopback0
ip address 1.1.1.1 255.255.255.0
ip ospf network point-to-point
interface FastEthernet0/0
ip address 10.0.0.1 255.255.255.0
ip ospf 1 area 1
interface FastEthernet1/0
ip address 13.0.0.1 255.255.255.0
ip ospf 1 area 1
router bgp 1
no synchronization
bgp log-neighbor-changes
network 1.1.1.0 mask 255.255.255.0
neighbor 10.0.0.2 remote-as 23
neighbor 10.0.0.2 route-map PRE-PEND out
neighbor 13.0.0.3 remote-as 23
no auto-summary
ip prefix-list JUST-1.1.1.0 seq 5 permit 1.1.1.0/24
route-map PRE-PEND permit 10
match ip address prefix-list JUST-1.1.1.0
set as-path prepend 1
route-map PRE-PEND permit 20
version 12.4R3:
hostname R2
interface FastEthernet0/0
ip address 10.0.0.2 255.255.255.0
ip ospf 1 area 1
interface FastEthernet0/1
ip address 23.0.0.2 255.255.255.0
ip ospf 1 area 1
router bgp 23
no synchronization
bgp log-neighbor-changes
neighbor 10.0.0.1 remote-as 1
neighbor 23.0.0.3 remote-as 23
no auto-summary
!
version 12.4Show commands R1:
hostname R3
interface FastEthernet0/0
ip address 13.0.0.3 255.255.255.0
ip ospf 1 area 1
interface FastEthernet0/1
ip address 23.0.0.3 255.255.255.0
ip ospf 1 area 1
router bgp 23
no synchronization
bgp log-neighbor-changes
neighbor 13.0.0.1 remote-as 1
neighbor 13.0.0.1 route-map SET-LOCAL-PREF in
neighbor 23.0.0.2 remote-as 23
no auto-summary
ip prefix-list LOCAL-PREF-250 seq 5 permit 1.1.1.0/24
route-map SET-LOCAL-PREF permit 10
match ip address prefix-list LOCAL-PREF-250
set local-preference 250
route-map SET-LOCAL-PREF permit 20
R1#show ip bgp summaryShow commands R2:
BGP router identifier 1.1.1.1, local AS number 1
BGP table version is 2, main routing table version 2
1 network entries using 120 bytes of memory
1 path entries using 52 bytes of memory
2/1 BGP path/bestpath attribute entries using 248 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
Bitfield cache entries: current 1 (at peak 2) using 32 bytes of memory
BGP using 452 total bytes of memory
BGP activity 2/1 prefixes, 2/1 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
10.0.0.2 4 23 77 73 2 0 0 00:29:01 0
13.0.0.3 4 23 74 74 2 0 0 00:29:01 0
R1#show ip bgp
BGP table version is 2, 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
*> 1.1.1.0/24 0.0.0.0 0 32768 i
R1#show ip route | begin resort
Gateway of last resort is not set
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
23.0.0.0/24 is subnetted, 1 subnets
O 23.0.0.0 [110/2] via 13.0.0.3, 00:48:43, FastEthernet1/0
[110/2] via 10.0.0.2, 00:48:09, FastEthernet0/0
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/0
13.0.0.0/24 is subnetted, 1 subnets
C 13.0.0.0 is directly connected, FastEthernet1/0
R2#show ip bgp summaryShow commands R3:
BGP router identifier 2.2.2.2, local AS number 23
BGP table version is 14, main routing table version 14
1 network entries using 120 bytes of memory
2 path entries using 104 bytes of memory
3/1 BGP path/bestpath attribute entries using 372 bytes of memory
2 BGP AS-PATH entries using 48 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
Bitfield cache entries: current 1 (at peak 2) using 32 bytes of memory
BGP using 676 total bytes of memory
BGP activity 1/0 prefixes, 4/2 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
10.0.0.1 4 1 73 77 14 0 0 00:29:07 1
23.0.0.3 4 23 71 73 14 0 0 01:04:54 1
R2#show ip bgp
BGP table version is 14, local router ID is 2.2.2.2
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
*>i1.1.1.0/24 13.0.0.1 0 250 0 1 i
* 10.0.0.1 0 0 1 1 i
R2#show ip route | begin resort
Gateway of last resort is not set
1.0.0.0/24 is subnetted, 1 subnets
B 1.1.1.0 [200/0] via 13.0.0.1, 00:28:37
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
23.0.0.0/24 is subnetted, 1 subnets
C 23.0.0.0 is directly connected, FastEthernet0/1
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/0
13.0.0.0/24 is subnetted, 1 subnets
O 13.0.0.0 [110/2] via 23.0.0.3, 00:48:16, FastEthernet0/1
[110/2] via 10.0.0.1, 00:49:19, FastEthernet0/0
R3#show ip bgp summaryBest wishes,
BGP router identifier 3.3.3.3, local AS number 23
BGP table version is 6, main routing table version 6
1 network entries using 120 bytes of memory
1 path entries using 52 bytes of memory
3/1 BGP path/bestpath attribute entries using 372 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
Bitfield cache entries: current 1 (at peak 2) using 32 bytes of memory
BGP using 600 total bytes of memory
BGP activity 1/0 prefixes, 5/4 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
13.0.0.1 4 1 74 74 6 0 0 00:29:09 1
23.0.0.2 4 23 73 71 6 0 0 01:04:56 0
R3#show ip bgp
BGP table version is 6, local router ID is 3.3.3.3
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
*> 1.1.1.0/24 13.0.0.1 0 250 0 1 i
R3#show ip route | begin resort
Gateway of last resort is not set
1.0.0.0/24 is subnetted, 1 subnets
B 1.1.1.0 [20/0] via 13.0.0.1, 00:28:39
3.0.0.0/24 is subnetted, 1 subnets
C 3.3.3.0 is directly connected, Loopback0
23.0.0.0/24 is subnetted, 1 subnets
C 23.0.0.0 is directly connected, FastEthernet0/1
10.0.0.0/24 is subnetted, 1 subnets
O 10.0.0.0 [110/2] via 23.0.0.2, 00:48:18, FastEthernet0/1
[110/2] via 13.0.0.1, 00:48:48, FastEthernet0/0
13.0.0.0/24 is subnetted, 1 subnets
C 13.0.0.0 is directly connected, FastEthernet0/0
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