DHCPv6-PD relay route injection - standard?

Sat May 18 07:51:04 UTC 2019

On 5/18/19 2:33 AM, Radu-Adrian Feurdean wrote:
> Those being said, I'm interested in how that feature is supported on gear that is not "subscriber-aware" (you were talking about Arista), since generating routing information from relayed DHCP(v6) is a big/important part of the "subscriber management" functionality.

What it does is hook into the DHCPv6 lightweight relay functionality. 
Basically, it just snoops the DHCPv6 replies for a PD assignment and 
inserts a quasi-static route into its table for anything that it sees 
with next-hop pointing at wherever the reply was going.  The static 
route is time-limited and gets removed when the delegation expires (or 
presumably if it sees a release of the corresponding resources).  It 
stores the database of those learned delegations, including expiry, in 
persistent memory so that it can re-install them in event of a reload. 
Obviously having good reltime information on the router is important for 
this.

The key here is that it doesn't care about "who" is getting the 
resources or why.  All it cares is that it saw a DHCPv6 reply via its 
relay that included a delegated prefix.

Juniper, at least, and presumably Cisco too, also implement a means to 
get that information via RADIUS.  That may be more what you're thinking of?

I'm not sure that the Cisco implementation I'm thinking of requires the 
BNG/BRAS features to be licensed.  See [1] under heading "DHCPv6 Relay 
Agent Notification for Prefix Delegation".  In particular, note:

> No user configuration is required for this feature. Static route management is done automatically by the relay agent.

It sounds like it operates similar to how I described above.  Basically, 
you can relegate your "subscriber management" to simple DHCP if such a 
lightweight implementation is sufficient for your needs.

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[1] 
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_dhcp/configuration/xe-3s/dhcp-xe-3s-book/ip6-dhcp-rel-agent-xe.pdf
-- 
Brandon Martin