| Previous | Table of Contents | Next |
Using EIGRP as the IGP
BGP-learned defaults are injected into EIGRP via redistribution. The 0/0 metric needs to be converted into an EIGRP-compatible metric by using the default-metric router command. RTA will inject its default with a high metric in such a way that the internal router (RTG) always gets a lower metric via RTF.
RTA configuration:
router eigrp 1
redistribute bgp 3 route-map DEFAULT_ONLY
passive-interface Serial0
network 172.16.0.0
default-metric 5 100 250 100 1500
router bgp 3
no synchronization
network 172.16.70.0 mask 255.255.255.0
network 172.16.220.0 mask 255.255.255.0
neighbor 172.16.20.1 remote-as 1
neighbor 172.16.20.1 filter-list 10 out
neighbor 172.16.50.1 remote-as 3
neighbor 172.16.50.1 route-map setlocalpref in
no auto-summary
ip as-path access-list 10 permit ^$
access-list 5 permit 0.0.0.0
route-map setlocalpref permit 10
set local-preference 300
route-map DEFAULT_ONLY permit 10
match ip address 5
RTA uses a route map DEFAULT_ONLY to match on the default route 0/0. Any other updates will be prevented from being redistributed into EIGRP. RTA also sets the metric by using the default-metric router command.
In the same manner, RTF is redistributing only the 0/0 into EIGRP using the route map DEFAULT_ONLY. RTF uses the default-metric 1000 100 250 100 1500 statement to set its default metric to an EIGRP-compatible metric. Note the bandwidth portion (1000) of the default-metric statement in RTF, which is much higher than the bandwidth (5) in RTA. This makes the metric from RTF much lower than the one from RTA.
RTF configuration:
router eigrp 1
redistribute bgp 3 route-map DEFAULT_ONLY
network 172.16.0.0
default-metric 1000 100 250 100 1500
router bgp 3
no synchronization
network 172.16.50.0 mask 255.255.255.0
neighbor 172.16.70.1 remote-as 3
neighbor 172.16.70.1 next-hop-self
neighbor 192.68.5.2 remote-as 2
neighbor 192.68.5.2 filter-list 10 out
no auto-summary
ip as-path access-list 10 permit ^$
access-list 5 permit 0.0.0.0
route-map DEFAULT_ONLY permit 10
match ip address 5
RTG is running EIGRP only and is following the default for all routes outside AS3.
RTG configuration:
router eigrp 1
network 172.16.0.0
The following is the IP routing table of RTG. Note that RTG follows the default toward RTF.
RTG#sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP,
M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF,
IA - OSPF inter area
N1 - OSPF NSSA external type 1,
N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2,
E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2,
* - candidate default U - per-user static route, o - ODR
Gateway of last resort is 172.16.50.1 to network 0.0.0.0
172.16.0.0/16 is subnetted, 4 subnets
D 172.16.220.0/24 [90/2195456] via 172.16.70.1, 00:12:17, Serial0
C 172.16.50.0/24 is directly connected, Serial1
D 172.16.20.0/24 [90/2681856] via 172.16.70.1, 00:12:17, Serial0
C 172.16.70.0/24 is directly connected, Serial0
D*EX 0.0.0.0/0 [170/3097600] via 172.16.50.1, 00:07:40, Serial1
Using IGRP as IGP
IGRP does not understand the 0.0.0.0 default. To set a default inside IGRP, the ip default-network global command needs to be set on RTA and RTF. The default network used needs to be redistributed into IGRP to set the default on the internal routers. A default-metric needs to be set for successful redistribution.
RTA is setting network 192.68.6.0/24 (or any other classfull network learned via BGP) to be the default network. RTA will redistribute that network only into IGRP.
RTA configuration:
router igrp 1
passive-interface Serial0
redistribute bgp 3 route-map DEFAULT_ONLY
network 172.16.0.0
default-metric 5 100 250 100 1500
router bgp 3
no synchronization
network 172.16.70.0 mask 255.255.255.0
network 172.16.220.0 mask 255.255.255.0
neighbor 172.16.20.1 remote-as 1
neighbor 172.16.20.1 filter-list 10 out
neighbor 172.16.50.1 remote-as 3
neighbor 172.16.50.1 route-map setlocalpref in
no auto-summary
ip default-network 192.68.6.0
ip as-path access-list 10 permit ^$
access-list 5 permit 192.68.6.0 0.0.0.255
route-map setlocalpref permit 10
set local-preference 300
route-map DEFAULT_ONLY permit 10
match ip address 5
RTF is also setting its default, to 192.68.6.0/24, and redistributing the default, with a better metric, into IGRP.
RTF configuration:
router igrp 1
redistribute bgp 3 route-map DEFAULT_ONLY
network 172.16.0.0
default-metric 1000 100 250 100 1500
router bgp 3
no synchronization
network 172.16.50.0 mask 255.255.255.0
neighbor 172.16.70.1 remote-as 3
neighbor 172.16.70.1 next-hop-self
neighbor 192.68.5.2 remote-as 2
neighbor 192.68.5.2 filter-list 10 out
no auto-summary
ip default-network 192.68.6.0
ip as-path access-list 10 permit ^$
access-list 5 permit 192.68.6.0 0.0.0.255
route-map DEFAULT_ONLY permit 10
match ip address 5
RTG is running IGRP only and is following the default for all routes outside AS3.
RTG configuration:
router igrp 1
network 172.16.0.0
The following is the IP routing table of RTG. Note that RTG follows the default toward RTF.
RTG#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP,
M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF,
IA - OSPF inter area
N1 - OSPF NSSA external type 1,
N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2,
E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2,
* - candidate default U - per-user static route, o - ODR
Gateway of last resort is 172.16.50.1 to network 192.68.6.0
I* 192.68.6.0/24 [100/8576] via 172.16.50.1, 00:00:32, Serial1
172.16.0.0/16 is subnetted, 4 subnets
I 172.16.220.0/24 [100/8576] via 172.16.70.1, 00:00:32, Serial0
C 172.16.50.0/24 is directly connected, Serial1
I 172.16.20.0/24 [100/10476] via 172.16.70.1, 00:00:32, Serial0
C 172.16.70.0/24 is directly connected, Serial0
| Previous | Table of Contents | Next |