[Xorp-users] Regular expressions in BGP policy

[Atanu Ghosh]

Hi,

The "show bgp routes" command shows the routes in the BGP RIB-IN we don't
remove filtered routes from the RIB-IN. The routes are left in the
RIB-IN to allow the user the change a policy, in which case all the
routes in the RIB-IN are refiltered. It is true that we should probably
annotate the route so that "show bgp routes" marks filtered routes.

If a route has been filtered then it won't be sent to the RIB or the BGP
peers, so the simple way to check is to run "show route table ipv4
unicast ibgp" or "show route table ipv4 unicast ebgp" depending on the
type of peering.

     Atanu.

>>>>> "Andreas" == Andreas Voellmy <andreas.voellmy at gmail.com> writes:

    Andreas> Hi,
    Andreas> I'm not sure how to match routes against an as-list regular expression
    Andreas> in bgp policy. I have a simple example that is not behaving as I
    Andreas> expect. In my example I have a single import policy, like this:

    Andreas> policy-statement imppol {
    Andreas> term impterm {
    Andreas> from {
    Andreas> as-path: "34567"
    Andreas> }
    Andreas> then {
    Andreas> trace: 4
    Andreas> reject
    Andreas> }
    Andreas> }
    Andreas> }


    Andreas> and I've connected this xorp router to another router, with AS 34567,
    Andreas> exporting a single route. I would expect that this route would match
    Andreas> the term in imppol, would be rejected, and would not be installed in
    Andreas> the bgp table of the receiver. From the tracing messages, it does look
    Andreas> like the route matches the term, and that the result is to reject the
    Andreas> route. HOWEVER, the route show up in my bgp table. Here is the trace
    Andreas> message when the route is received:

    Andreas> SubnetRoute:
    Andreas> Net: 10.10.11.0/24
    Andreas> PAList:
    Andreas> Next Hop Attribute 128.36.229.113
    Andreas> Origin Path Attribute - IGP
    Andreas> AS Path Attribute AsPath: [AS/34567]
    Andreas> Multiple Exit Descriminator Attribute: MED=0
    Andreas> Local Preference Attribute - 100: rejected
    Andreas> Basic VarRW trace:
    Andreas> Read 14: AsPath: [AS/34567]
    Andreas> Write 0: 4
    Andreas> Read 14: AsPath: [AS/34567]
    Andreas> Write 0: 4
    Andreas> Execution trace:
    Andreas> Running policy: imppol
    Andreas> Running term: impterm
    Andreas> PUSH txt 34567
    Andreas> LOAD 14: AsPath: [AS/34567]
    Andreas> REGEX
    Andreas> ONFALSE_EXIT: true
    Andreas> PUSH u32 4
    Andreas> STORE 0: 4
    Andreas> REJECT
    Andreas> Outcome of term: Reject
    Andreas> Outcome of policy: Reject
    Andreas> Outcome of whole filter: Reject
    Andreas> End of trace

    Andreas> And Here is my BGP route table:

    >> show bgp routes
    Andreas> Status Codes: * valid route, > best route
    Andreas> Origin Codes: i IGP, e EGP, ? incomplete

    Andreas> Prefix                Nexthop                    Peer            AS Path
    Andreas> ------                -------                    ----            -------
    Andreas> *  10.10.11.0/24         128.36.229.113             128.36.229.113  34567 i

    Andreas> I would greatly appreciate it if someone could point out what I've
    Andreas> done wrong here. Thanks!

    Andreas> Regards,
    Andreas> Andreas Voellmy

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