Category Archives: bgp

BGP Route Refresh in JUNOS

What happens when you change a BGP import routing policy in your neighbor configuration? Changes take effect immediately or we need to issue the soft-inbound command to request the routes? Let’s see by an example.

We received the route 10.83.0.0/24 from 10.82.1.9 already as you see below.

Now I change the local preference from 2000 to 1999 in the import policy and commit the config.

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BGP open message receives a TCP RST

On this micro post, I would like to show one reason why a BGP open message receives a TCP RST. For this test, I set up a BGP neighborship between two peers: PeerA(10.82.1.9) and PeerB(10.82.1.10)

PeerA initiates the connection and look what happens in the packet capture.

bgp-open-reset

According to the sequence, TCP seems to have established properly. 3WAY handshake is done and PeerA thinks it can send its capabilities in its OPEN message and it actually sends it but something weird happens. Remote side PeerB first closes the connection [FIN,ACK] and then sends a RST segment to our OPEN message but why does he do that?

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BGP: Connection collision resolution

I was doing couple of tests on BGP protocol today between two EBGP peers and monitoring the BGP trace file I enabled on my Junos box during which I have seen the following NOTIFICATION being sent by one of the peers.

I don’t recall of having seen this BGP NOTIFICATION before actually. Looking at RC4271 reveals why this occurs.

To prevent further race conditions like this from happening in the future, apparently setting the option “passive” for one of the peer allows us not to initiate BGP connection from both peers but only from active side.

Quagga and SRX BGP communication

Since the gated daemon, IGP/EGP software has evolved tremendously. I had used zebra long time ago but now to better manage my lab network I wanted to use quagga BGP and OSPF daemons. Quagga is spectacular and
its syntax is almost the same like Cisco IOS. After having used JunOS for 2 years, it is a bit difficult to switch to cisco CLI. I want to write this post because of a problem I encountered during BGP communication between quagga and an SRX/JunOS device as I am not that familiar with quagga.

I configured quagga BGP like below

and configured SRX like this;

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Why is BGP route not advertised?

There may be several reasons why a BGP route isn’t advertised to its eBGP neighbor in JUNOS. I was doing some tests and noticed that one of my routes 172.16.10.0 isn’t advertised to its neighbor.

Show route indicates that route is also learned via OSPF as well due to my crap topology at the moment:) and doesn’t choose it as BGP best route.

inactive-path option also clearly indicates a problem with the preference.

If a route isn’t advertised, it is good to check with the detail option!