IOS XE 15.5
IOS XR 5.3
The topology for this demo:
In this post we will be taking a look at EIGRP and Site of Origin, like BGP, this is used to manipulate how we will route via backdoor links vs how we route over MPLS. Our demo will focus on R3 and XR1 as the PEs and R7 and R12 as the CE.
Site of Origins job is to help control how we learn routing updates, and prevent feedback on the wrong links during recovergence. We will configure a new backdoor link between R7 and R12 and run EIGRP over that link, we'll also use EIGRP to peer with the PEs. The idea is to use the backdoor link and to not use the MPLS circuit. I don't normally recommend using backdoor links in this manner, getting high speed P2P connectivity between sites today is relatively easy.
So the idea here is to prefer the Backdoor path and not the MPLS link.
R7
R7#sh ip route vrf EIGRP eigrp | b Gateway
Gateway of last resort is not set
59.0.0.0/24 is subnetted, 1 subnets
D 59.0.0.0 [90/15360] via 37.0.0.3, 00:07:12, GigabitEthernet1.37
83.0.0.0/24 is subnetted, 1 subnets
D 83.0.0.0 [90/15360] via 37.0.0.3, 00:07:12, GigabitEthernet1.37
90.0.0.0/24 is subnetted, 1 subnets
D 90.90.90.0 [90/16000] via 37.0.0.3, 00:07:12, GigabitEthernet1.37
106.0.0.0/24 is subnetted, 1 subnets
D 106.0.0.0 [90/15360] via 37.0.0.3, 00:07:12, GigabitEthernet1.37
113.0.0.0/24 is subnetted, 1 subnets
D 113.0.0.0 [90/15360] via 37.0.0.3, 00:07:12, GigabitEthernet1.37
131.0.0.0/24 is subnetted, 1 subnets
D 131.0.0.0 [90/15360] via 37.0.0.3, 00:07:12, GigabitEthernet1.37
172.16.0.0/32 is subnetted, 2 subnets
D 172.16.12.12 [90/10880] via 12.7.0.12, 00:07:12, GigabitEthernet1.127
D EX 192.168.100.0/24 [170/16000] via 37.0.0.3, 00:07:12, GigabitEthernet1.37
D 192.168.112.0/24 [90/15360] via 37.0.0.3, 00:07:12, GigabitEthernet1.37
[90/15360] via 12.7.0.12, 00:07:12, GigabitEthernet1.127
R7#traceroute vrf EIGRP 172.16.12.12 num
Type escape sequence to abort.
Tracing the route to 172.16.12.12
VRF info: (vrf in name/id, vrf out name/id)
1 12.7.0.12 4 msec * 2 msec
The irony of this configuration is that the current RIB won't change much, what will happen is the way the updates are learned. From R7s perspective, it knows to reach R12's loopback via the backdoor link, if the backdoor link, with not EIGRP SoO configured, would be learned over the MPLS network. 99% of cases this would be acceptable for failover/HA requirements. If this is not desirable, then SoO would be a solution. So the above output to prove that R7 will use the backdoor link is valid, but from a failover perspective, if the BD went away, so would that route. This is because XR1 will propagate the route to R3 but since SoO is configured, that route won't get propagated to R7.
R3
route-map EIGRP_SOO permit 10
set extcommunity soo 90:90
!
interface GigabitEthernet1.37
encapsulation dot1Q 37
ip vrf sitemap EIGRP_SOO
XR1
router eigrp CCIE
vrf EIGRP
address-family ipv4
interface GigabitEthernet0/0/0/0.121
site-of-origin 90:90
RP/0/0/CPU0:XR1#sh eigrp vrf EIGRP topology 172.16.7.7/32 | b Extended
Sat Jan 14 16:56:48.171 UTC
Extended Community:
SoO:90:90
R3#$dress-family ipv4 vrf EIGRP topology 172.16.12.12/32 | b Extended
Extended Community: SoO:90:90
As you can see, the updates on R3 learn about R12s loopback and XR1 sees R7s loopback, mind you these are the non-directly connected CE sites. This shows that the SoO was propagated and honored.
This is pretty much the configuration. Any additional route updates that are received from the CE will be dropped on the outgoing PE to the remote CE.
Thanks for stopping by!
Rob Riker, CCIE #50693
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