What is an EVPN Type 5 Route for (EVPN/VXLAN)

For EVPN/VXLAN, Type 5 routes are used for two purposes: Internally and Externally

Internally it’s used to communicate which VTEPs have a given subnet instantiated on it.

Here’s an example of the output of the command show ip bgp route-type ip-prefix ipv4 on an Arista cEOS spine running EVPN/VXLAN.

It’s showing you that 10.1.10.0/24 (VLAN 10/VNI 10010) is only available on leaf1 and leaf2 (10.1.255.1-2) and 10.1.20.0/24 (VLAN 20/VNI 10020) is only available on leaf3 and leaf4 (10.1.255.3-4). It’s eBGP so each leaf has its own ASN (you see in the path field). The next hop shows the VTEP IP (10.1.254.1-4). I checked on the spine as the spine receives all the EVPN routes from the leafs and propagates them as a route server. The spines don’t install any of these routes, they just propagates them.

       Network                Next Hop              Metric  LocPref Weight  Path

 * >      RD: 10.1.255.1:10000 ip-prefix 10.1.10.0/24
                                 10.1.254.1            -       100     0       65101 i
 * >      RD: 10.1.255.2:10000 ip-prefix 10.1.10.0/24
                                 10.1.254.2            -       100     0       65102 i
 * >      RD: 10.1.255.3:10000 ip-prefix 10.1.20.0/24
                                 10.1.254.3            -       100     0       65103 i
 * >      RD: 10.1.255.4:10000 ip-prefix 10.1.20.0/24
                                 10.1.254.4            -       100     0       65104 i

This is important for to know when trying to find a host who’s MAC or MAC-IP isn’t known. Let’s say you’re on leaf1 on VLAN 10, and there’s a host you’re trying to ping on VLAN 50. In Arista cEOS with symmetric IRB, the internal Type 5 routes are generated under the tenant VRF with “redistribute connected”.

   vrf Blue
      rd 10.1.255.2:10000
      route-target import evpn 10000:10000
      route-target export evpn 10000:10000
      redistribute connected

On leaf3 and 4, I’m going to remove that redistribute connected command, then see what the spines see.

          Network                Next Hop              Metric  LocPref Weight  Path
 * >      RD: 10.1.255.1:10000 ip-prefix 10.1.10.0/24
                                 10.1.254.1            -       100     0       65101 i
 * >      RD: 10.1.255.2:10000 ip-prefix 10.1.10.0/24
                                 10.1.254.2            -       100     0       65102 i

So for 10.1.20.0/24, we have no prefix information. Any VLAN 20 to VLAN 20 communication will work, any you can communicate with a host in VLAN 20 from outside of VLAN only if the host has talked and a Type 2 route was generated. But if there’s no reachability information, the fabric doesn’t have a way to find it without the Type 5 route information. So if they talk, the fabric will discover them. If the host is silent, the Type 5 route is needed.

Right now there’s a host at 10.1.20.201 on VLAN 20. From a host on 10.1.10.0/24, I’ll try to ping 10.1.20.201.

host1#ping 10.1.20.201
PING 10.1.20.201 (10.1.20.201) 72(100) bytes of data.
From 10.1.10.1 icmp_seq=1 Destination Net Unreachable

I’ll turn the Type 5 routes back on.

host1#ping 10.1.20.201
PING 10.1.20.201 (10.1.20.201) 72(100) bytes of data.
80 bytes from 10.1.20.201: icmp_seq=1 ttl=62 time=11.8 ms
80 bytes from 10.1.20.201: icmp_seq=2 ttl=62 time=3.34 ms
80 bytes from 10.1.20.201: icmp_seq=3 ttl=62 time=2.18 ms
80 bytes from 10.1.20.201: icmp_seq=4 ttl=62 time=2.04 ms
80 bytes from 10.1.20.201: icmp_seq=5 ttl=62 time=1.95 ms

The fabric had enough information now to find the hosts because the Type 5 routes were there.

So that’s internally. What about externally?

On leaf3 I configured an external router, R1, for BGP on the tenant VRF.

leaf3#show ip bgp summary vrf Blue 
BGP summary information for VRF Blue
Router identifier 10.1.20.1, local AS number 65103
Neighbor Status Codes: m - Under maintenance
  Neighbor V AS           MsgRcvd   MsgSent  InQ OutQ  Up/Down State   PfxRcd PfxAcc
  10.1.5.0 4 1                 25        37    0    0 00:16:20 Estab   1      1
From this BGP session, leaf3 has learned the route 172.16.0.0/12. 
B E      172.16.0.0/12 [200/0]
           via 10.1.5.0, Ethernet12

But that route is only learned on leaf3, how do we get it to the other leafs? Type 5. Again the result of show bgp evpn route-type ip-prefix ipv4:

          Network                Next Hop              Metric  LocPref Weight  Path
(A bunch of other routes)
* >      RD: 10.1.255.3:10000 ip-prefix 172.16.0.0/12
                                 10.1.254.3            -       100     0       65103 1 i

This tells the fabric that the network 172.16.0.0.12 is available on leaf3 (65103). If a host anywhere else on the fabric needs to send a packet to that network, encap the VXLAN packet and send it to leaf3.

Now a host connected to leaf1 can ping 172.16.0.1, which is outside of the EVPN/VXLAN fabric.

host1#ping 172.16.0.1
PING 172.16.0.1 (172.16.0.1) 72(100) bytes of data.
80 bytes from 172.16.0.1: icmp_seq=1 ttl=62 time=2.98 ms
80 bytes from 172.16.0.1: icmp_seq=2 ttl=62 time=1.57 ms
80 bytes from 172.16.0.1: icmp_seq=3 ttl=62 time=1.64 ms
80 bytes from 172.16.0.1: icmp_seq=4 ttl=62 time=1.62 ms
80 bytes from 172.16.0.1: icmp_seq=5 ttl=62 time=1.80 ms