Exploring the quirks of Network Engineering
Scenario
EIGRP uses variance for load-balancing and distribute-lists (IOS) and route-policies (XR) for filtering. This section covers a simple setup with an EIGRP configured router filtering a couple of /30 transit links and with variance configured for load-balancing.
IOS Config
hostname R1
!
router eigrp 10
variance 2
network 10.10.12.0 0.0.0.3
network 10.10.42.0 0.0.0.3
network 192.168.50.0
passive interface GigabitEthernet1/0
distribute-list prefix BLOCK_TRANSIT_LINKS in
no auto-summary
eigrp router-id 2.2.2.2
!
ip prefix-list BLOCK_TRANSIT_LINKS seq 5 deny 10.10.13.0/30
ip prefix-list BLOCK_TRANSIT_LINKS seq 10 deny 10.10.43.0/30
ip prefix-list BLOCK_TRANSIT_LINKS seq 50 permit 0.0.0.0/0 le 32
!
interface GigabitEthernet0/0
description link to R2
ip address 10.10.12.2 255.255.255.252
speed 100
full-duplex
!
interface GigabitEthernet0/1
description link to R4
ip address 10.10.42.2 255.255.255.252
speed 100
full-duplex
!
interface GigabitEthernet0/2
description Local LAN
ip address 192.168.50.1 255.255.255.0
speed 100
full-duplex
XR Config
hostname R1
!
interface GigabitEthernet0/0/0/0
description link to R2
ipv4 address 10.10.12.2 255.255.255.252
speed 100
duplex full
!
interface GigabitEthernet0/0/0/1
description link to R4
ipv4 address 10.10.42.2 255.255.255.252
speed 100
duplex full
!
interface GigabitEthernet0/0/0/2
description Local LAN
ipv4 address 192.168.50.1 255.255.255.0
speed 100
duplex full
!
prefix-set BLOCK_TRANSIT_LINKS
10.10.13.0/30,
10.10.43.0/30
end-set
!
route-policy TRANSIT_FILTER
if destination in BLOCK_TRANSIT_LINKS then
drop
else
pass
endif
end-policy
!
router eigrp 10
address-family ipv4
router-id 2.2.2.2
variance 2
route-policy TRANSIT_FILTER in
!
interface GigabitEthernet0/0/0/0
!
interface GigabitEthernet0/0/0/1
!
interface GigabitEthernet0/0/0/2
passive-interface
!
!
!