> -----Original Message----- > From: [email protected] [mailto:juniper-nsp- > [email protected]] On Behalf Of Eric Van Tol > Sent: Wednesday, September 29, 2010 2:57 PM > To: juniper-nsp > Subject: Re: [j-nsp] L2VPN MTU Issue > > Well, primary credit goes to JTAC, but doing some packet captures, I found > that the packets entering the customer interface were not leaving the router. > JTAC suggested 1520, but that only allowed 1498-bytes through. I bumped it > up to 1524, which still did not work, so then I bumped it up to 1528. I am > still not too keen on the math, but JTAC hasn't broken it down for me yet. > If anyone out there knows, please point me to a reference. I googled like > mad yesterday, but either overlooked the obvious, or wasn't searching for the > right info. > > -evt
I was reading a partial thread yesterday in the archives and for whatever reason, could not find the reference thread and today, I came upon this: http://puck.nether.net/pipermail/juniper-nsp/2006-September/007000.html "In a typical l2 vpn there would be two labels added; vrf and outer transport. The core interfaces will need an mtu of ethernet (1500) + vlan (4) + martini encap (0 | 4) + labels (8) + what ever link encap is needed based on core interface type. If the core interfaces are also ethernet then this is another 14 for total of 1526-1530 (the latter is with optional martini control word)" I came up with 1504 + 8 + 14 = 1526 in this calculation. I am 2 bytes over the necessary, but to be honest, I will probably bump it up to 1530 or higher, so that 802.1q encapsulation can be supported. For anyone starting out in MPLS VPNs in the Juniper world, this thread is a good one to read, as Harry points out at least one (perhaps previously, now) undocumented function of the MPLS MTU later on in one of his responses. Thanks, Harry! -evt _______________________________________________ juniper-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/juniper-nsp
