Routing Configuration Guide, Cisco IOS XE Catalyst SD-WAN Release 17.x
Describes how static route configuration impacts BFD session establishment and how correct next-hop resolution ensures reliable BFD operation in transport VPNs.
For BFD to work correctly, the next-hop IP address must be known and reachable. Static routes configured incorrectly can cause BFD session failures.
Do not configure static routes pointing directly to Ethernet (non-P2P) interfaces without specifying a next-hop IP. This causes BFD failures because the next-hop IP is unknown.
For Ethernet interfaces using DHCP, ensure the DHCP server provides the router IP. Then use either the DHCP-learned route or configure a static route with the dhcp keyword to dynamically resolve the next-hop IP. For more information on DHCP server and client configurations, see Configuring the Cisco IOS XE DHCP Server and Configuring the Cisco IOS XE DHCP Client.
For point-to-point (P2P) interfaces, such as cellular, you can configure static routes that point directly to the interface.
In P2P networks, the remote BFD endpoint is always a single hop away with no intermediate devices.
In non-P2P networks, the remote BFD endpoint is typically multiple hops away, with the next hop being only the first of several intermediate hops.
| Exit interface type | Static route format | BFD support | Description |
|---|---|---|---|
| Ethernet (Non-P2P) |
ip route 0.0.0.0 0.0.0.0 GigabitEthernetX |
Not supported |
Next-hop IP unknown; causes BFD failure. Use next-hop IP or DHCP-based static route. |
| Ethernet (Non-P2P) |
ip route 0.0.0.0 0.0.0.0 <next-hop IP> |
Supported |
Recommended when next-hop IP is static and known. |
| Ethernet (Non-P2P) |
ip route 0.0.0.0 0.0.0.0 dhcp or ip route 0.0.0.0 0.0.0.0 GigabitEthernetX dhcp |
Supported |
For DHCP interfaces; dynamically resolves next-hop IP from DHCP server. |
| Point-to-Point (P2P) |
ip route 0.0.0.0 0.0.0.0 CellularX |
Supported |
Fully supported static route format for BFD. |
To verify the installation and next-hop resolution of static default routes regardless of whether the route uses a next-hop IP address, DHCP-resolved next hop, or a directly connected interface use the show ip route command.
For these configurations below:
ip route 0.0.0.0 0.0.0.0 10.0.0.1
ip route 0.0.0.0 0.0.0.0 172.16.0.1Verify the routing table for transport VPN:
Device# show ip route
S* 0.0.0.0/0 [1/0] via 10.0.0.1
[1/0] via 172.16.0.1
Device#For this configuration below:
ip route 0.0.0.0 0.0.0.0 dhcpVerify the routing table for transport VPN:
Device# show ip route
S* 0.0.0.0/0 [1/0] via 192.168.0.1
Device#For this configuration below:
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/0/1 dhcpVerify the routing table for transport VPN:
Device# show ip route
S* 0.0.0.0/0 [1/0] via 192.168.0.1, GigabitEthernet0/0/1
Device#
For this configuration below:
ip route 0.0.0.0 0.0.0.0 Cellular0/0/0Verify the routing table for transport VPN:
Device# show ip route
S* 0.0.0.0/0 is directly connected, Cellular0/0/0
Device#
For these configurations below:
ip route 0.0.0.0 0.0.0.0 Cellular0/0/0
ip route 0.0.0.0 0.0.0.0 dhcpVerify the routing table for transport VPN:
Device# show ip route
S* 0.0.0.0/0 is directly connected, Cellular0/0/0
[1/0] via 192.168.0.1
Device#