[c-nsp] MTU on MPLS TE Tunnels w/PA-FE-TX?

[Rodney Dunn]

I'll ask. The same CEF/MPLS code improvements that went in to 12.2SB and
other 12.2S child branches are coming to 12.4T or 12.5T and this may be part of
it. 

On Sun, Mar 18, 2007 at 11:08:49PM -0400, Vinny Abello wrote:
> Nope, I think what I have wrong is is I'm not running an S train or that Cisco has not put those fixes in any mainline code yet. I checked a few routers that do have SB trains and it seems to work properly although I didn't do a complete test on them yet. I need to get some time to test more in a lab scenario.
> 
> Is there any chance those fixes will be ported into any mainline code? The routers I was testing on were running 12.2(40) and I also checked on a 12.3(22) version and saw the same problem. My 12.2(28)SB6 router has no problems with it though and I can adjust the MTU above 1500 bytes on a PA-FE-TX or I/O-2FE with no problems. Most of our routers run mainline. The ones that run SB are just for special features or more specifically certain combinations of features we can't get anywhere else... unless this is going to be another one of those features.
> 
> Rodney Dunn wrote:
> >> I found some things in the archives about people complaining the PA-FE-TX is limited in hardware to 1500 byte MTU, but then I found other people saying it should work fine with MPLS tagged packets as long as you specify the size with tag-switching mtu or mpls mtu, which I have done without success. I know the PA-FE-TX will refuse to be configured manually for any other size MTU larger than 1500, so I'm leaning towards it being a hardware limitation. The tunnel interface even shows an MTU of 1496 in the output of show mpls interfaces detail. It initially appears to come up as 1514 but then drops to 1496.
> >>
> > 
> > CSCsc62963 [QDDTS] [CCO]
> > Internally found severe (Sev2) bug: Resolved (R)
> > Have configurable MTU Range 1500 -1530 on PA-1FE and PA-2FE
> > 
> > Fixed in 12.2(28)SB and 12.2(31)SB.
> > 
> > IIRC max SDU size is 1530 bytes on the wire.
> > 
> > TE is just a label stack and if it's native IP only 4 bytes.
> > 
> > I think you have something else wrong. 
> > 
> > What does your configurations look like and topology.
> > 
> > Rodney
> > 
> >  
> >> There isn't a whole lot of documentation on this other than use mpls mtu if you're using ethernet... Most MPLS documents assume you're using POS or Gig-e where you wouldn't really need to worry about it.
> >>
> >> Can someone comment on this an indicate if there is a FastEthernet interface type on a 7200 that will support a larger MTU size for MPLS TE tunnels to pass 1500 byte packets or if there is a way to make the PA-FE-TX work and pass MPLS tagged packets larger than 1500 bytes? I know I could use the PA-GE but that quickly eats bandwidth points, or I could use NPE-G1 or NPE-G2 interfaces, but I don't have either engine presently and they are expensive propositions just to fix an MTU problem.
> >>
> >>
> >> Thanks for any insight!
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