AS PATH limits

William Herrin bill at
Fri Dec 22 19:30:06 CST 2017

On Fri, Dec 22, 2017 at 12:40 PM, Nick Hilliard <nick at> wrote:

> What router software version are you running that barfs on long as-paths?

Hi Nick,

Versions of quagga up until the very most recent release corrupt the
transmission of routes with very long AS paths. They add up the packet
length wrong. The neighbors of any router brand then barf on the malformed
data and terminate the BGP session.

Your peer running quagga must either upgrade or filter long AS paths or you
will receive corrupt data and terminate the BGP session. There's nothing
that -you- can do about it.

The AS path lengths we're talking about are unreasonable. They indicate a
high probability of misconfiguration at the origin. There's no legitimate
cause for them to exist on the pubic Internet at all. It would be
reasonable to treat them like when peers offer /32 prefixes and just say no.

Bill Herrin

William Herrin ................ herrin at  bill at
Dirtside Systems ......... Web: <>

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