IGP (OSPF/ISIS) adjacency will go down after inet family is removed from GRE tunnel

This article explains why protocols running over Generic Routing Encapsulation (GRE) go down once the inet family is removed from GRE. This is expected behavior.

Before Deactivating Family INET on gr interface:

After deactivating family INET on gr interface:

IPv4 is in broken state for GRE as shown in above command, as there is no family configured for ifl 331 (gr interface) for the incoming ISIS packets encapsulated in IP header.

For this reason, the packets will not be hitting the GR interface.

L2 CSNP packets are getting dropped in the kernel when the inet family is deactivated on the GR interface. When a packet is sent for decapsulation, the GRE code checks for ‘inet’ family on the IFL. Since the deactivation deletes the family, the GRE code discards the packet by ticking noroute counter.

After the inet family is removed from the GRE, there will not be any IFF (IFL) associated in PFE for forwarding traffic. This is an expected behavior.

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