Punt/Glean Adjacency

mistabrumley89

Anyone have a link to a detailed description of these? Haven't really ran into anything of my liking.

SecurityThroughObscurity

glean - destinations are attached to multi-access media, for which MAC rewrite string are unavailable.
for example, router directly connected to a subnet with multiple hosts. so it maintains a prefix for the subnet instead of individual host prefixes - the subnet prefix pointed to a glean adj. when packets arrived the adjacency table is gleaned for the specific prefix.
punt - special handling when CEF is not supported for the packets

lrb

The book called "Cisco Express Forwarding" is your best bet but this DOC isn't too bad How to Choose the Best Router Switching Path for Your Network - Cisco

As a bit of a side note, CEF glean adjacencies are also critical to how DMVPN Phase 2 works to enable spoke-to-spoke comms. The router purposely marks the entry in the FIB as glean so that when the first packet needs to be sent spoke-to-spoke, it triggers an NHRP resolution request to map the public IP address to the internal IP address that advertised the route.

mistabrumley89

Thanks for the responses. Pretty spot on for what I was looking for. Brownie points.