Subnet Size for BGP peers.
Barton F Bruce
barton at gnaps.com
Wed Jul 29 23:22:27 CDT 2009
----- Original Message -----
From: "Jim Wininger" <jbotctc at gmail.com>
To: <nanog at nanog.org>
Sent: Wednesday, July 29, 2009 3:59 PM
Subject: Subnet Size for BGP peers.
> I have a question about the subnet size for BGP peers. Typically when we
> turn up a new BGP customer we turn them up on a /29 or a /30. That seems
> be the "norm".
> We connect to many of our BGP peers with ethernet. It would be a simple
So what is wrong with a /31? We use /30s but if you are short on IP space,
look at using /31 rather than /30 links. Cuts your space usage in half.
If I remember correctly, the BIG problem with using /31s when they first
became "legal" was to decide if the customer still gets the higher numbered
IP address (or you the lower one), or if you still get the ODD number. No
kidding, it is a problem for some!
Where you are on ethernet, use a seperate 802.1q vlan per customer and have
your switch give the customer untagged packets. If you have downstreams in
your COLO, and either free or as a paid service, offer to setup private
vlans in your switch for any pair or group of customers that need to also
connect to each other privately for whatever they are doing. In that latter
case, they will be getting tagged packets but their routers or switches
should have no problem dealing with them.
We don't charge for physical crossconnects, so this has saved us having to
do physical crossconnects between customers, and has saved customers router
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