Routing

I am testing out a very simple scenario.

R7------eBGP--------R1------iBGP-----------R2------eBGP------------R4

R7 and R4 are in AS 7

R1 and R2 are in AS 1234

The original scenario I was testing was for as_override.

Essentially, R7 introduces a route 7.0.0.0/8, advertises it to R1 which advertises it to R2.

What I was expecting, and the JNCIS study guide supports this, was for R2 to not perform any sanity checks on AS_PATH and advertise the route to R4, even though the AS_PATH then would have been 1234 7.

I was then expecting R4 to actually reject the NLRI after checking for 7 in the AS_PATH. But what I am noticing is that R2 seems to have a sanity check and does not advertise the NLRI with AS_PATH 7 to R4 in the first place.

nbhasin@R2# run show route protocol bgp 

inet.0: 22 destinations, 22 routes (22 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

7.0.0.0/8          *[BGP/170] 00:23:34, localpref 100, from 150.1.1.1
                      AS path: 7 I
                    > to 192.168.12.1 via em0.12

<SNIP>

nbhasin@R2# run show bgp summary                      
Groups: 2 Peers: 2 Down peers: 0
Table          Tot Paths  Act Paths Suppressed    History Damp State    Pending
inet.0                 1          1          0          0          0          0
Peer                     AS      InPkt     OutPkt    OutQ   Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
150.1.1.1              1234         57         55       0       0       23:55 1/1/1/0              0/0/0/0
192.168.24.4              7          6          7       0       0        1:58 0/0/0/0              0/0/0/0

[edit]
nbhasin@R2# run show route advertising-protocol bgp 192.168.24.4 

[edit]
nbhasin@R2# 

 Now when I add the as-override keyword to the configuration, R2 starts advertising the route.

nbhasin@R2# show protocols bgp 
traceoptions {
    file BGP;
    flag all;
}
group SUB_AS_64512 {
    type internal;
    neighbor 150.1.1.1 {
        local-address 150.1.2.2;
    }
}
group EBGP_PEERS {
    type external;
    neighbor 192.168.24.4 {
        peer-as 7;
    }
}

nbhasin@R2# set protocols bgp group EBGP_PEERS as-override 

[edit]
nbhasin@R2# commit 
commit complete

[edit]
nbhasin@R2# run show route advertising-protocol bgp 192.168.24.4    

inet.0: 22 destinations, 22 routes (22 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 7.0.0.0/8               Self                                    1234 I

 Other implentations of BGP (not Junos) I have worked with do not display this behavior. The loop prevention is performed on the receiver not on the sender.

Can anyone confirm if my observations are confirmed and if so, when did this behavior change in Junos? I am using the following version :-

nbhasin@R2# run show version | match "Base OS" 
JUNOS Base OS boot [12.1R1.9]
JUNOS Base OS Software Suite [12.1R1.9]

 Thanks in advance,

Nic

On a related note, if the observations above are correct, in a completely Junos based infrastructure, would the "loops" command have any use left?

Nic

Hi there,

Check out the "advertise-peer-as" knob

http://www.juniper.net/techpubs/software/junos/junos94/swconfig-routing/disabling-suppression-of-route-advertisements.html#id-13255463 

HTH

Thanks
Alex

Alex,

That knob did the trick. Thank you so much and kudos.

[edit]
nbhasin@R2# run show route advertising-protocol bgp 192.168.24.4    

[edit]
nbhasin@R2# set protocols bgp group EBGP_PEERS advertise-peer-as    

[edit]
nbhasin@R2# commit 
commit complete

[edit]
nbhasin@R2# run show route advertising-protocol bgp 192.168.24.4    

inet.0: 22 destinations, 22 routes (22 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 7.0.0.0/8               Self                                    7 I

[edit]
nbhasin@R2# 

Nic