Data Center

IMPORTANT MODERATION NOTICE

This community is currently under full moderation, meaning  all posts will be reviewed before appearing in the community. Please expect a brief delay—there is no need to post multiple times. If your post is rejected, you'll receive an email outlining the reason(s). We've implemented full moderation to control spam. Thank you for your patience and participation.



Expand all | Collapse all

How to deal with AS Loop in my topology ?

  • 1.  How to deal with AS Loop in my topology ?

    Posted 09-15-2021 23:20
    If I have the following topology:

    bgp.evpn.0: 27 destinations, 43 routes (22 active, 0 holddown, 21 hidden)
    2:192.168.1.3:3::10::00:05:86:71:dc:03/304 MAC/IP (2 entries, 0 announced)
             BGP                 /-101
                    Route Distinguisher: 192.168.1.3:3
                    Next hop type: Indirect, Next hop index: 0
                    Address: 0xc6341b0
                    Next-hop reference count: 20
                    Source: 192.168.1.44
                    Protocol next hop: 192.168.1.3
                    Indirect next hop: 0x2 no-forward INH Session ID: 0x0
                    State: <Hidden Int Ext>
                    Local AS: 65535 Peer AS: 64511
                    Age: 2:40       Metric2: 0
                    Validation State: unverified
                    Task: BGP_64511_64511.192.168.1.44+179
                    AS path: 65535 I
                    Communities: target:10:10 encapsulation:vxlan(0x8)
                    Import
                    Route Label: 10
                    ESI: 00:00:00:00:00:00:00:00:00:00
                    Localpref: 100
                    Router ID: 192.168.1.44
                    Hidden reason: AS path loop
                    Secondary Tables: vpn1.evpn.0
                    Indirect next hops: 1
                            Protocol next hop: 192.168.1.3 Metric: 0
                            Indirect next hop: 0x2 no-forward INH Session ID: 0x0
                            Indirect path forwarding next hops: 1
                                    Next hop type: Router
                                    Next hop: 10.20.1.1 via ge-0/0/5.0
                                    Session Id: 0x140
                                    192.168.1.3/32 Originating RIB: inet.0
                                      Metric: 0     Node path count: 1
                                      Forwarding nexthops: 1
                                            Nexthop: 10.20.1.1 via ge-0/0/5.0
                                            Session Id: 140
    ​

    How to avoid this AS loop ?  
    as-override ?

    family inet unicast loops 1 ?


    Where is the best place to apply this ?

    thanks !!



  • 2.  RE: How to deal with AS Loop in my topology ?

    Posted 09-16-2021 16:11
    Different tools exist, I do prefer as-override as the mechanism, but the question is: Where is the loop in your topology? I see that both ASes are different: 65535 and 65534.

    Elvin


  • 3.  RE: How to deal with AS Loop in my topology ?

    Posted 09-17-2021 05:32
    Hi ,

    Good day !
    To accept routes coming from the same AS (loop)

    1 > unicast loops (this needs to be configured onCE device )to accept the routes when the PE is not directly connected between the sites that have the same AS ie if the PE receives a routes from the same AS number as it is peered with it will not advertise the routes to the peer hence in this case unicast loop is used when there are multiple hops involved 

    EX : https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/ref/statement/loops-edit-routing-options-autonomous-system.html 

    2> as-override (this is usually configured on the PE ) it replaces peer AS number in the incoming routes with its own 

    EX: https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/ref/statement/as-override-edit-protocols-bgp.html

    NOTE : looking at the diagram i would say as-override is a better option but it depends on your design also 

    -Sharanya


  • 4.  RE: How to deal with AS Loop in my topology ?

    Posted 09-17-2021 10:33
    Thank you for correcting the diagram, now it is applicable.  : )

    The as-override option is my preferred one, since it avoids you accepting looping ASN inbound for all sessions globally, and the as-override is applicable to a single peer, so it scope is not as wide as accepting looping ASN from all peers. The looping option is good when there is a stub connection, usually.

    Elvin


  • 5.  RE: How to deal with AS Loop in my topology ?

    Posted 09-17-2021 01:11
    Sorry, I uploaded a wrong diagram. I corrected it.

    thanks !!


  • 6.  RE: How to deal with AS Loop in my topology ?

    Posted 09-17-2021 12:14
    thanks so much !!


  • 7.  RE: How to deal with AS Loop in my topology ?

    Posted 09-17-2021 12:14
    thanks so much !!


  • 8.  RE: How to deal with AS Loop in my topology ?

    Posted 09-17-2021 14:52
    I have the following topology:
    I did not get the following as loop

    thanks for coaching !!!


  • 9.  RE: How to deal with AS Loop in my topology ?

    Posted 09-17-2021 21:37
    Glad it helped.

    Regards,

    Elvin