Routing

 View Only
last person joined: 2 hours ago 

Ask questions and share experiences about ACX Series, CTP Series, MX Series, PTX Series, SSR Series, JRR Series, and all things routing, including portfolios and protocols.
  • 1.  Routing Loop

    This message was posted by a user wishing to remain anonymous
    Posted 10-30-2022 07:34
    This message was posted by a user wishing to remain anonymous

    Hi Community 

    need some help with a issue we faced in the network , we deleted IBGP and OSPF between Router 2 to to Router 5 , after which router 2 didnt had router present for 2.2.2.2. and we started to have traffic from Router 1  (source 1.1.1.1) ECMP'ed toward  2.2.2.2 , next hop Router 2 and Router 3  as OSPF costs matched , which cause intermittent outage.
    As when the packets reached router 2 , there was no route present for 2.2.2.2 and traffic started to loop between router 1 and router 2. While the packets which were sent via Router 3 were fine.

    Is there any way we can over come this issue, any feature which could help in this , dont want to add static routes 

    Network Topology


  • 2.  RE: Routing Loop

    Posted 10-30-2022 07:40
    I'm having some trouble following the issue.

    There are two router 5 in the diagram but I think the router 5 in question is the one where 2.2.2.2 is an external interface.

    The missing information is the state of the active routing tables for the 2.2.2.2 route during the problem and when the link is working on
    router 1
    router 2
    router 3

    I suspect the issue has to do with whether the route is in both bgp and ospf or only one at the time the link advertisement during the link lost state.  I think the bgp policy on router 1 or router 2 may be changing routing priority in a way that creates the loop during link failure.  But the routing table status is needed to confirm when the loop happens in which protocol then the configuration can determine why the priorities are in the loop format seen.

    ------------------------------
    Steve Puluka BSEET - Juniper Ambassador
    IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP - Retired)
    http://puluka.com/home
    ------------------------------



  • 3.  RE: Routing Loop

    This message was posted by a user wishing to remain anonymous
    Posted 10-31-2022 13:51
    This message was posted by a user wishing to remain anonymous

    updated with topology and routing info


  • 4.  RE: Routing Loop

    This message was posted by a user wishing to remain anonymous
    Posted 10-30-2022 12:26
    This message was posted by a user wishing to remain anonymous

    Updated the diagram , in terms of routing table 

    on R1 -

    BGP Route present for 2.2.2.2/32  next hop Router 2 (before the cutover)
    BGP Route present for 2.2.2.2/32 next hop Router 2  +Router 3 (After the cutover,ECMP due to equal cost)

    R2
    BGP Route present for 2.2.2.2/32  next hop Router 5 (before the cutover)
    BGP Route NOT present for 2.2.2.2  (After the cutover)

    the trace route from R1
    1.1.1.1 -->R1-->R2---(Following bigger subnet 2.0.0.0/24)

    Network Topo

    ---->R1---(OSPF Cost equal between R2 and R3)---> R2 -->R1(loop)




  • 5.  RE: Routing Loop

    Posted 11-01-2022 06:47
    What you are seeing with the loss of the bgp route is due to iBGP standard behavior.  To avoid route loops only local routes are sent to ibgp peers.

    Thus iBGP does require either a full mesh of all peers each other or the use of route reflectors to distribute the full routing table to all sites if that is needed.

    Your topology would probably be a typical route reflector on router 2 & 3 with each other site 4,5,6 remote and 1 core peering to both route reflectors for redundancy.


    ------------------------------
    Steve Puluka BSEET - Juniper Ambassador
    IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP - Retired)
    http://puluka.com/home
    ------------------------------



  • 6.  RE: Routing Loop

    This message was posted by a user wishing to remain anonymous
    Posted 11-02-2022 06:37
    This message was posted by a user wishing to remain anonymous

    Is there any way we can avoid next hop which does not have route present.. post cutover ?

    Agreed on RR but not quite possible in our scenario


  • 7.  RE: Routing Loop

    This message was posted by a user wishing to remain anonymous
    Posted 11-02-2022 06:38
    This message was posted by a user wishing to remain anonymous

    what i mean to say was that we cannot deploy RR in our environment and currently dont have as well , so is there any other way ?


  • 8.  RE: Routing Loop

    Posted 11-02-2022 06:40
    Edited by spuluka 11-02-2022 06:40
    If you can't do the route reflector or a full mesh peering the best alternative is to switch from iBGP to eBGP and just assign a different ASN from the private range 64512 to 65534 to each router.

    Then all the distribution will occur as you are expecting to the other sites.

    ------------------------------
    Steve Puluka BSEET - Juniper Ambassador
    IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP - Retired)
    http://puluka.com/home
    ------------------------------