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San_man
San_man
Explorer
May 15, 2023
Solved

eBGP routes not showing up

  • May 15, 2023
  • 3 replies
  • 11477 views

Hi,

I am doing a lab setup where I have hit a problem with ebgp routes disappearing from the routing-database when ibgp routes shows up. I have not done any route manipulation on my BGP session at the moment. I would have thought that even if the route is not active it would appear in the routing-database (get router info routing-table database). I can see the routes being advertised and also received (get router info routing-table bgp neigh received-routes). 

The BGP sessions are over the tunnel and I am assuming that there would not be any difference.

Any help is appreciated. 

 

San

Best answer by srajeswaran

Fortigate adds below config by default to set local-preference to 100.

 

FGT # config router bgp

FGT (bgp) # show full | grep local-pre
set default-local-preference 100

 

IBGP carries the local-prefernce values within same AS and due to that reason you get route with local-preference 100 and thats the reason IBGP route is getting activated.

 

You can either set the "set default-local-preference 0" on the advertising device (IBGP neighbor) or apply a route-map in the receiving fortigate to make local-preference 0 for IBGP or another route-map to increase the local-preference to 200 for EBGP route.

 

 

3 replies

srajeswaran
Staff
srajeswaran
Staff
May 15, 2023

Can you check if you are hitting the scenario given in https://community.fortinet.com/t5/FortiGate/Technical-Tip-BGP-routes-not-added-into-the-routing-table-when/ta-p/194698

 

This article is about BGP and OSPF, but I think  EBGP and IBGP are similar scenario

    San_man
    San_manAuthor
    Explorer
    May 15, 2023

    Hi Suraj, 

    This is slightly different. 

    In the example both routes are visible in the routing database (#get router info routing-table database), but in my case the eBGP route is not visible in the database when the iBGP is learned. I am trying to learn default route from eBGP peer and iBGP peer. 

    However, when I do #get router info bgp network --> I can see all the learned routes there. In the output below there are 2 default route from iBGP and 1 from eBGP (neighbour 203.116.1.5). The local preference for the iBGP is 100 but the eBGP does not have any - could that be the reason? Weigh and metric is the same. 

     

    here is the output:

    Origin codes: i - IGP, e - EGP, ? - incomplete

    Network Next Hop        Metric LocPrf Weight RouteTag Path
    *>i0.0.0.0/0  172.21.1.1    0   100        0            0 i <256/1>
    *>i                172.22.1.1    0   100        0            0 i <256/2>
    *                   203.116.1.5  0    0           0            65111 i <-

    akristof
    Staff
    akristof
    Staff
    May 15, 2023

    Hello,

    Even if you will change local-pref for eBGP route, at some point if all metrics are the same, eBGP route will win over iBGP route.

      Yurisk
      SuperUser
      Yurisk
      SuperUser
      May 15, 2023

      Hi,

      you mean your FGT gets the same routes both - via eBGP and iBGP? AD of eBGP is 20 while of iBGP is 200, so unless you do some manipulation on FGT (redistribute, route-map assigning weight etc. to the learned routes) this should not be possible.  

       

      Personal opinion: I've seen bugs and problems with routing protocols in FGT over years, but not like that, and is strongly inclined that something in setup/configuration is causing this, not FGT itself.

        San_man
        San_manAuthor
        Explorer
        May 15, 2023

        Hi Yuri, 

        Yeah I will have a further look at my configuration. I was also hoping that the eBGP route would be installed as well. On the advertising FTGT I have tried capability-default-originate to redistribute static just to see if that matters as well and played with few other configs. The BGP is over a tunnel but I don't think that would matter. 

         

        Here is the neighbor config on the router that is receiving the route. 203.116.1.5 neighbor is external and the second neighbor is internal.  

        edit "203.116.1.5"
        set soft-reconfiguration enable
        set interface "Prisma"
        set remote-as 65111
        set keep-alive-timer 10
        set holdtime-timer 30
        set connect-timer 5
        set update-source "Prisma"
        next

        config neighbor
        edit "172.21.1.1"
        set next-hop-self enable
        set soft-reconfiguration enable
        set interface "Spoke-HUB1"
        set remote-as 65001
        set keep-alive-timer 10
        set holdtime-timer 30
        set connect-timer 5
        set update-source "Spoke-HUB1"
        set additional-path both
        set adv-additional-path 8

         

        I will have a second look at the config. 

         

        san

        srajeswaran
        Staff
        srajeswaran
        Staff
        May 16, 2023

        Interesting behavior. I tested the same and I can see the IBGP route is preferred by default and we need to apply a route-map to increase the local-preference of EBGP route to make it preferred.

        I will update if I manage to find the  possible reasons for this behavior.

          Yurisk
          SuperUser
          Yurisk
          SuperUser
          May 16, 2023

          Exactly - it means nothing - iBGP/eBGP for the Fortigate (as well as any other gear - Cisco/Juniper/etc) as long as the Local preference of a route is higher than the other one. 

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