[j-nsp] Adjusting MSS size for GRE tunnels in JunOS

[Harry Reynolds]

Wanting to add that the MTU workaround also used the
clear-dont-fragment-bit command, which is an ASP feature that is not
available on ordinary tunnel services pic.

http://www.juniper.net/techpubs/software/junos/junos63/swconfig63-interf
aces/html/interfaces-adaptive-services-config6.html

With this option you can avoid issues with the end-to-end application
never seeing an ICMP MTU too large error, and therefore retransmitting a
packet that is too large, while the default action of not allowing
fragmentation prevents successful communications.

Regards

 

> -----Original Message-----
> From: Harry Reynolds 
> Sent: Wednesday, November 30, 2005 7:02 PM
> To: 'Terry Rodery'; 'juniper-nsp at puck.nether.net'
> Subject: RE: [j-nsp] Adjusting MSS size for GRE tunnels in JunOS
> 
> AFAIK, not at this time. The TCP MSS is a system-wide 
> parameter, and JUNOS software does not support adjustment:
> 
> jnpr at foo> start shell
> % sysctl -A | grep mss
> net.inet.tcp.mssdflt: 512
> net.inet.tcp.v6mssdflt: 1024
> net.inet.tcp.send_mssdflt: 0
> 
> 
> It is not recommended that folks mess with this type of 
> system default. I have heard that some folks have found a 
> work-around by increasing GRE tunnel MTU (say to 1600).
> 
> HTHs
> 
>   
> > -----Original Message-----
> > From: juniper-nsp-bounces at puck.nether.net 
> > [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of 
> Terry Rodery
> > Sent: Wednesday, November 30, 2005 1:51 PM
> > To: juniper-nsp at puck.nether.net
> > Subject: [j-nsp] Adjusting MSS size for GRE tunnels in JunOS
> > 
> > Hi,
> > 
> > I'm curious to know if JunOS on the M-series is capable of 
> > doing that same as Cisco's "ip tcp adjust-mss 1436" on a 
> > tunnel interface.  I've done a bit of looking around and so 
> > far I've only seen it mentioned for JunOS for ERX.  Anyone 
> > have any idea or could possible point me in the right direction? :)
> > 
> > Regards,
> > Terry Rodery
> > 
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> > 
>