[j-nsp] BGP Hold time expiry

[Richard A Steenbergen]

On Sun, Oct 05, 2008 at 01:48:41PM +0200, Daniel Roesen wrote:
> On Fri, Sep 19, 2008 at 08:36:25AM -0500, Richard A Steenbergen wrote:
> > Juniper includes all L2 overhead
> 
> Not really. For Ethernet, Juniper does NOT include the 4 octets FCS
> (frame checksum). So Cisco 1500 == Juniper 1514, not 1518 as one might
> guess. Now enable vlan-tagging on the Juniper Ethernet interface, and
> default MTU readout will say 1518 - which is 1514 plus 4 for the VLAN
> tag.
> 
> Yes, MTU stuff makes a grown man cry.

I didn't say otherwise. We're talking L2 headers not L2 wire overhead,
things like FCS, preamble, etc generally don't count under either Cisco
or Juniper. Under Juniper you define the physical MTU, and then L2
headers due to framing and vlans start getting whittled off as they're
used.  Cisco 1500 would be Juniper 1514 on an untagged interface, 1518
on tagged, or 1522 on double/stacked/flexible-tagged. 

The annoyance is not only that Cisco and Juniper numbers mean different
things, but that you end up having to consider how you're using the
interface and must remember to change your MTUs when you change your
tagging.

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)