NCS540 won't isntall DHCP-sourced default route into its RT

[dandreye-luk]

Hi All,

My customer has an NCS540's interface Gi0/0/0/1 configured with "ip address dhcp" alone to act as a DHCP client:

interface GigabitEthernet0/0/0/1
  ip address dhcp

It gets what looks like a perfectly valid DHCP response from the server with the IP address/mask 10.1.1.72/24 and successfully adopts it, and default GW IP 10.1.1.1 too, which it won't install into its routing table for some reason, even though 10.1.1.1 is visible in the "show ip dhcp lease" output. Is there some nuance we're missing by chance? What exactly may be preventing it from installing 10.1.1.1 into the RT? With "debug ip dhcp ipv4" (and term mon enabled) there's no debug output at all; we also tried adding various other debugs like "debug ip routing", "debug ip error", "debug ip event" and still no debug output whatsoever upon plugging in the Gi0/0/0/1's cable into the DHCP server. We tried commiting "no ip address" and then "ip address dhcp" on the interface to ensure it starts from scratch, still no luck.

We have no default route defined anywhere in the config, and no dynamic routing protocols are used.

IIRC the NCS540 is running some 7.11.x version dated August 2024.

Many thanks in anticipation!

[tkarnani]

to confirm the nexthop address is being received you should be able to see it in "show dhcp ipv4 client detail"

however in ios-xr the installation of a gateway of last resort is not available, you will need to manually configure the static route if one is required.

[dandreye-luk]

@tkarnani:

Thank you for a quick reply. 

> to confirm the nexthop address is being received you should be able to see it in "show dhcp ipv4 client detail"

We saw it there too besides the "show dhcp lease" output, so it's definitely being received.

> however in ios-xr the installation of a gateway of last resort is not available, you will need to manually configure the static route if one is required.

It's a gateway of last resort **obtained via DHCP** implied here, right? Is there any particular reason behind such implementation?