[j-nsp] Loopback IP address in BGP Peering

C T crtrio2003 at yahoo.com
Sun Mar 1 15:34:42 EST 2009

Just to add a comment.
Some people confuse it, including me sometimes... :-)
Even a router or a system with Classfull (without CIDR) the address z.y.x.0 or z.y.x.255 can be considered valid host addresses.
For instance, if you have a class B (CIDR equivalent of
The addresses: is a valid host address is a valid host address
But using class C, the .255 and .0 are invalid host addresses.
Good reference at: http://tools.ietf.org/html/rfc4632
Claus T
>All major vendors support 0 and 255 as loopback in the last octet. o if >you are using J or C for instance, your safe. If you use an obscure >small vendor, the choice to use 0 and 255 can come back and bite >you in the ***.
>Mark Tinka wrote:
> On Saturday 28 February 2009 06:31:15 pm Cougar wrote:
>> What kind of exception is this? In CIDR world you can use any address 
>> you like except first and last _LAN_ addresses when netmask is /30 or 
>> less. With /31 and /32 can use any address and so far I haven't seen 
>> any problems using x.x.x.0 or x.x.x.255 in Junipers.
> That may very well be - but my suggestion is just because it can be 
> done, doesn't mean it's a great idea "all around".
> These are the types of practices that come back and bite you due to 
> varying levels of support for implementing .0 and
> .255 across various pieces of software. I'm not presuming the OP has 
> only Junipers to deal with in their network.
> Given the number of addresses one may potentially save in, say, a /24 
> sliced only for Loopbacks vs. not getting stressed by why this may 
> break some things in the network; I'd much rather sacrifice those two 
> addresses, thank-you- very-much.
> Keep it simple, keep it stupid, keep it unambiguous. The physics don't 
> change, just how you apply them.
> Then again, to each his own...
> You probably want to spend some time wading through:
> http://tinyurl.com/dzw4cj
> http://tinyurl.com/av8rwm
> http://tinyurl.com/chwjms
> Mark.
> ----------------------------------------------------------------------
> --
> _______________________________________________
> juniper-nsp mailing list juniper-nsp at puck.nether.net 
> https://puck.nether.net/mailman/listinfo/juniper-nsp


More information about the juniper-nsp mailing list