Task 5.1 BGP

The task states that SW1 and SW4 should not run bgp,but should get the bgp routes via defult route of R1.So we should redistribute bgp into ospf on R1.

But the solution has nothing with this part.

There`s also a local preference configuration in the SG which is not asked in the task.

What do you think of these two problems?

thanks

Comments

  • We do have to redistribute on R1 in order for SW1 and SW4 to get reachability to BGP prefixes. here is why:

     

    • R1 is getting BGP prefixes from R2 and R5. By default R1 is choosing R2 as the exit point because the WEIGHT, AS-PATH, LOCAL PREF, MED and all other attributes are the same; hence R1 is choosing R2 because it has a lower router id (150.X.2.2) compared to R5 

     

    • Before any changes if R1 tries to ping to any BGP prefix, it will not have reachability because R1 will send the traffic to to SW1 to get to R2 and SW1 will blackhole the traffic.

     

    • We have 2 choices to fix this issue:
      • set a higher weight on R1 for R5 like 200, which I did. By setting a higher weight on R1 for R5, R1 will use R5 as the exit point
      • Set a higher local pref on R5, which the Solution guide did. By setting the local pref on R5, R1 will use R5 because it has a higher local pref compared to R2 which has a default local pref of 100

     

    •  With either of those configs done, R1 will have reachablility to BGP prefixes through R5. Hence SW2 and SW4 will also have reachability to BGP prefixes because of their default generated by R1 (ref  Task 4.14).

     

    I hope it helps. It's too bad I just deleted all my configs to do Volume 3 Lab 8. I could have used snag it to show you the outputs. [:D]

     

  • HI,  I Didnt configure nothing special, because BGP Prefixes in Router One prefers R5 path because of the lower IGP metric to the next Hop. This was made in TASK 4:12.

    In My case: !

    Task 4:12

    interface Vlan27
     ip address 144.1.27.7 255.255.255.0
     ip ospf cost 1000
    end

    !!!!!!!!!!!!!!

    Rack1R1#show ip bgp 28.119.16.0
    BGP routing table entry for 28.119.16.0/24, version 2
    Paths: (2 available, best #1, table Default-IP-Routing-Table)
      Advertised to update-groups:
         1        
      100 54, (Received from a RR-client)
        150.1.5.5 (metric 20) from 150.1.5.5 (150.1.5.5)
          Origin IGP, metric 0, localpref 100, valid, internal, best
      100 54, (Received from a RR-client)
        150.1.2.2 (metric 1002) from 150.1.2.2 (150.1.2.2)
          Origin IGP, metric 0, localpref 100, valid, internal

    Please, let me know is this is correct.

    regards.

    Horacio

    .

  • Agree with hfarias, I didn't have to do anything and it worked without any special modifications. Also I made R1 peer with R2 inestead of R5. I don't see any reason for not doing that.

    Tom

  • Same here. No need to redistribute anything if your IGP is set up correctly to prefer the route through R5. We also note that by using the loopbacks to establish peering between AS100 and AS200, we can also remove the need for any local preference manipulation since the prefered path will always be through R5 unless it looses it's connection to R4.

    Eric

  • Hi,

    Not too sure what exactly is happening, but what I can see is that following the SG works fine (though I used loopbacks to setup my neibour peers). However when I shutdown the session between R5 and R4. connectivity is lost and a trace just loops between SW1 and R1. 

    Note that on the (call it primary path) via R5 so R1 => R5 => R4 => R3, all these devices run BGP. However, on the path via R2, SW1 doesn't run BGP and so will blackhole traffic.

    Thoughts please??

    Crownade

  • Yes, I agree with your explanation.... all seems correct.....

     

    However...no restrictions have been placed to get the connectivity and also it's not specified that the traffic should prefer R5 as exit point....

     

    thus I've had a different approach and actualy setup 2 tunnels  to compensate for the non-bgp speaking device SW1 in AS200....

    thus the first tunnel between R1 and R2...... for BGP transit traffic via SW1.....

    the second tunnel between R1 and SW2....

    These tunnels I've made part of OSPf area 0 ans set the cost lower so that the tunnels are prefered via the IGP....

     

    Also, as no local IGP prefix's where adverticed via BGP I redistributed OSPF into R1 for ping reachability tests.....

    and after this SW1/SW4 van reach R1/R5 via the default route..... thus as non BGP speakers they also can have reachabilityb towards the BGP prefixes....

    Thus ...traffic can now either transit via R2 or R5...depending on BGP bestpath selection to get to the BGP domain

    Hope this make sense.


    RSRack7R1#i

    Interface                  IP-Address      OK? Method Status                Protocol

    FastEthernet0/0            144.7.17.1      YES manual up                    up

    Serial0/0                  unassigned      YES manual up                    up

    Serial0/0.1                144.7.15.1      YES manual up                    up

    Serial0/1                  unassigned      YES manual administratively down down

    Loopback0                  150.7.1.1       YES manual up                    up

    Tunnel12                   150.7.1.1       YES TFTP   up                    up

    Tunnel18                   150.7.1.1       YES TFTP   up                    up

    RSRack7R1#cr

    router ospf 1

     log-adjacency-changes

     area 1 virtual-link 150.7.7.7

     default-information originate always

     distribute-list route-map FILTER_R2 in

    router bgp 200

     no synchronization

     bgp log-neighbor-changes

     redistribute ospf 1

     neighbor 144.7.15.5 remote-as 200

     neighbor 144.7.15.5 route-reflector-client

     neighbor 150.7.2.2 remote-as 200

     neighbor 150.7.2.2 ebgp-multihop 255

     neighbor 150.7.2.2 update-source Loopback0

     neighbor 150.7.2.2 route-reflector-client

     neighbor 150.7.8.8 remote-as 200

     neighbor 150.7.8.8 update-source Loopback0

     neighbor 150.7.8.8 route-reflector-client

     no auto-summary

    alias exec cr sh run | s router

    RSRack7R1#br

    BGP table version is 24, local router ID is 150.7.1.1

    Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

                  r RIB-failure, S Stale

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

     

       Network          Next Hop            Metric LocPrf Weight Path

    * i28.119.16.0/24   150.7.4.4                0    100      0 100 54 i

    *>i                 144.7.24.4               0    100      0 100 54 i

    * i28.119.17.0/24   150.7.4.4                0    100      0 100 54 i

    *>i                 144.7.24.4               0    100      0 100 54 i

    * i112.0.0.0        150.7.4.4                0    100      0 100 54 50 60 i

    *>i                 144.7.24.4               0    100      0 100 54 50 60 i

    * i113.0.0.0        150.7.4.4                0    100      0 100 54 50 60 i

    *>i                 144.7.24.4               0    100      0 100 54 50 60 i

    * i114.0.0.0        150.7.4.4                0    100      0 100 54 i

    *>i                 144.7.24.4               0    100      0 100 54 i

    * i115.0.0.0        150.7.4.4                0    100      0 100 54 i

    *>i                 144.7.24.4               0    100      0 100 54 i

    * i116.0.0.0        150.7.4.4                0    100      0 100 54 i

    *>i                 144.7.24.4               0    100      0 100 54 i

    * i117.0.0.0        150.7.4.4                0    100      0 100 54 i

    *>i                 144.7.24.4               0    100      0 100 54 i

    * i118.0.0.0        150.7.4.4                0    100      0 100 54 i

       Network          Next Hop            Metric LocPrf Weight Path

    *>i                 144.7.24.4               0    100      0 100 54 i

    * i119.0.0.0        150.7.4.4                0    100      0 100 54 i

    *>i                 144.7.24.4               0    100      0 100 54 i

    *> 144.7.5.0/24     144.7.15.5              65         32768 ?

    *> 144.7.15.0/24    0.0.0.0                  0         32768 ?

    *> 144.7.17.0/24    0.0.0.0                  0         32768 ?

    *> 144.7.27.0/24    144.7.17.7               2         32768 ?

    *> 144.7.78.0/24    144.7.17.7               2         32768 ?

    *> 150.7.1.0/24     0.0.0.0                  0         32768 ?

    *> 150.7.2.2/32     144.7.17.7               3         32768 ?

    *> 150.7.4.0/24     144.7.15.5             129         32768 ?

    *> 150.7.5.5/32     144.7.15.5              65         32768 ?

    *> 150.7.7.7/32     144.7.17.7               2         32768 ?

    *> 150.7.8.8/32     144.7.17.7               3         32768 ?

    *> 192.10.7.0       150.7.8.8                2         32768 ?

    RSRack7R1#trace 28.119.16.1

     

    Type escape sequence to abort.

    Tracing the route to 28.119.16.1

     

      1 150.7.2.2 4 msec 4 msec 4 msec

      2 144.7.24.4 28 msec 28 msec 28 msec

      3 144.7.34.3 28 msec 32 msec 32 msec

      4 204.12.7.254 32 msec *  60 msec

    RSRack7R1#


    RSRack7SW1#trace 28.119.16.1


    Type escape sequence to abort.

    Tracing the route to 28.119.16.1


      1 144.7.17.1 0 msec 0 msec 9 msec

      2 150.7.2.2 0 msec 0 msec 0 msec

      3 144.7.24.4 33 msec 34 msec 33 msec

      4 144.7.34.3 42 msec 34 msec 50 msec

      5 204.12.7.254 34 msec *  25 msec

    RSRack7SW1#i

    Interface              IP-Address      OK? Method Status                Protocol

    Vlan1                  unassigned      YES manual administratively down down

    Vlan17                 144.7.17.7      YES manual up                    up

    Vlan27                 144.7.27.7      YES manual up                    up

    FastEthernet0/1        unassigned      YES unset  up                    up

    FastEthernet0/2        unassigned      YES unset  down                  down

    FastEthernet0/3        unassigned      YES unset  up                    up

    FastEthernet0/4        unassigned      YES unset  down                  down

    FastEthernet0/5        unassigned      YES unset  up                    up

    FastEthernet0/6        unassigned      YES unset  down                  down

    FastEthernet0/7        unassigned      YES unset  down                  down

    FastEthernet0/8        unassigned      YES unset  down                  down

    FastEthernet0/9        unassigned      YES unset  down                  down

    FastEthernet0/10       unassigned      YES unset  down                  down

    FastEthernet0/11       unassigned      YES unset  down                  down

    FastEthernet0/12       unassigned      YES unset  down                  down

    FastEthernet0/13       unassigned      YES manual up                    up

    FastEthernet0/14       unassigned      YES manual up                    up

    FastEthernet0/15       unassigned      YES manual up                    up

    FastEthernet0/16       unassigned      YES unset  up                    up

    FastEthernet0/17       unassigned      YES unset  up                    up

    FastEthernet0/18       unassigned      YES unset  up                    up

    FastEthernet0/19       unassigned      YES unset  up                    up

    FastEthernet0/20       unassigned      YES unset  up                    up

    FastEthernet0/21       unassigned      YES unset  up                    up

    FastEthernet0/22       unassigned      YES unset  down                  down

    FastEthernet0/23       unassigned      YES unset  down                  down

    FastEthernet0/24       unassigned      YES unset  down                  down

    GigabitEthernet0/1     unassigned      YES unset  down                  down

    GigabitEthernet0/2     unassigned      YES unset  down                  down

    Port-channel1          144.7.78.7      YES manual up                    up

    Loopback0              150.7.7.7       YES manual up                    up

    RSRack7SW1#sh run | i bgp

    alias exec bs sh ip bgp sum

    alias exec br sh ip bgp

    RSRack7SW1#





    RSRack7SW2#pi 28.119.16.1


    Type escape sequence to abort.

    Sending 5, 100-byte ICMP Echos to 28.119.16.1, timeout is 2 seconds:

    !!!!!

    Success rate is 100 percent (5/5), round-trip min/avg/max = 59/65/75 ms

    RSRack7SW2#

    RSRack7SW2#

    RSRack7SW2#

    RSRack7SW2#

    RSRack7SW2#

    RSRack7SW2#

    RSRack7SW2#

    RSRack7SW2#

    RSRack7SW2#i

    Interface              IP-Address      OK? Method Status                Protocol

    Vlan1                  unassigned      YES manual administratively down down

    Vlan82                 192.10.7.8      YES manual up                    up

    FastEthernet0/1        unassigned      YES unset  down                  down

    FastEthernet0/2        unassigned      YES unset  up                    up

    FastEthernet0/3        unassigned      YES unset  down                  down

    FastEthernet0/4        unassigned      YES unset  up                    up

    FastEthernet0/5        unassigned      YES unset  down                  down

    FastEthernet0/6        unassigned      YES unset  up                    up

    FastEthernet0/7        unassigned      YES unset  down                  down

    FastEthernet0/8        unassigned      YES unset  down                  down

    FastEthernet0/9        unassigned      YES unset  down                  down

    FastEthernet0/10       unassigned      YES unset  down                  down

    FastEthernet0/11       unassigned      YES unset  down                  down

    FastEthernet0/12       unassigned      YES unset  down                  down

    FastEthernet0/13       unassigned      YES manual up                    up

    FastEthernet0/14       unassigned      YES manual up                    up

    FastEthernet0/15       unassigned      YES manual up                    up

    FastEthernet0/16       unassigned      YES unset  up                    up

    FastEthernet0/17       unassigned      YES unset  up                    up

    FastEthernet0/18       unassigned      YES unset  up                    up

    FastEthernet0/19       unassigned      YES unset  up                    up

    FastEthernet0/20       unassigned      YES unset  up                    up

    FastEthernet0/21       unassigned      YES unset  up                    up

    FastEthernet0/22       unassigned      YES unset  down                  down

    FastEthernet0/23       unassigned      YES unset  down                  down

    FastEthernet0/24       unassigned      YES unset  up                    up

    GigabitEthernet0/1     unassigned      YES unset  down                  down

    GigabitEthernet0/2     unassigned      YES unset  down                  down

    Port-channel1          144.7.78.8      YES manual up                    up

    Loopback0              150.7.8.8       YES manual up                    up

    Tunnel18               150.7.8.8       YES unset  up                    up

    RSRack7SW2#cr

    sh run | s router

             ^

    % Invalid input detected at '^' marker.


    RSRack7SW2#sh runn  | b router bgp

    router bgp 200

     no synchronization

     bgp log-neighbor-changes

     neighbor 150.7.1.1 remote-as 200

     neighbor 150.7.1.1 transport path-mtu-discovery

     neighbor 150.7.1.1 update-source Loopback0

     no auto-summary


     

  • Same here. No need to redistribute anything if your IGP is set up correctly to prefer the route through R5. We also note that by using the loopbacks to establish peering between AS100 and AS200, we can also remove the need for any local preference manipulation since the prefered path will always be through R5 unless it looses it's connection to R4.

    This is very interesting task though i had to raise the local preferece on R5 inorder from bgp prefixes to take path via R5. The default route on R1 is magical here the routers not running ospf take the advantage of default routes to reach to forward bgp prefixes while bgp routers already have the bgp longest match prefix.

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