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Hello,
Does this help?
https://www.juniper.net/documentation/en_US/junos/information-products/topic-collections/release-notes/16.1/m-mx-t-series-toc.html
<https://www.juniper.net/documentation/en_US/junos/information-products/topic-collections/release-notes/16.1/m-mx-t-series-toc.html#jd0e11155>
Support for unique AS path count ( MX Series)—Starting with Junos OS
Release 16.1R4, you can configure a routing policy to determine the
number of unique autonomous systems (ASs) present in the AS path. The
unique AS path count helps determine whether a given AS is present in
the AS path multiple times, typically as prepended ASs. In earlier Junos
releases it was not possible to implement this counting behavior using
theas-pathregular expression policy. This feature permits the user to
configure a policy based on the number of AS hops between the route
originator and receiver. This feature ignores ASs in theas-paththat are
confederation ASs, such asconfed_seqandconfed_set.
To configure AS path count, include theas-path-unique-countcount(equal |
orhigher | orlower)configuration statement at the[edit policy-options
policy-statementpolicy_namefrom]hierarchy level.
Thanks
Alex
On 13/09/2019 00:18, Andy Litzinger wrote:
Hi All,
I thought this would be in a cookbook somewhere but I can't find it. Is
there a way to write an as-path regex so it will match a providers ASN
(e.g. 1234) one or more times and then 1 or 2 more ASNs zero or more
times? I'm hoping to be able to account for AS prepending.
I'm an Enterprise network and one of my upstream ISPs is sending me full
routes + default. I want to filter the routes down to networks that are
directly connected or at most 2 hops away from my ISP, but also allow for
AS prepending. It's the prepending that is tripping me up or else I think
this would suffice: "^1234+ .{0,2}"
I think with cisco you can do this with backreferences, but Junos doesn't
seem to support those.
TIA,
-andy
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