To conclude this introduction to BGP
let's have a look at how the router
displays the BGP status and the BGP
table. First off we'll have a look at IPv4.
This is on Cisco IOS and the summary
displayed on the screen in front of you
shows quite a lot of useful information
about the BGP neighbor status.
First off you have a column listing
the IP addresses of the neighbors.
It then displays the BGP version number.
We use BGP version 4 today
as you have already learned. And then lists
the autonomous system number,
the messages received and sent. So these are
the updates that have been sent by the
router and received by the router from
each individual neighbor.
The table version indicates any changes.
So it's an incremental counter of the changes
in the BGP table. And then you have two
columns showing the input queue and
output queue; the queues of the updates
which are waiting to be processed.
These queues are normally 0 but if the router
is under load or you're trying to
transfer a large BGP table you'll
sometimes see values in these queues.
The next column shows how long the peering
is up or shows how long the peering is down.
And the state up or down is shown
in the final column. If you see numbers
there that shows how many prefixes have
been received. If you see status messages
like "no connect" and so forth then the
peering is considered done.
So the screen in front of you shows
the IPv4 version of this. For IPv6
the display is actually very similar
again we have a list of the neighbors.
This time the v6 addresses as well as
BGP version number, AS number,
and all the different messages, and
the number of prefixes received.
If you look near the top
of the router display it
also indicates things like the BGP
router identifier which is a unique 32-bit
integer identifying the router
as well as the AS number
and various other details about
how much memory is needed,
how many network entries there are
and so forth.
And then looking at the next
table on the screen in front of you
the "show ip bgp" output displays the BGP table
and this is an excerpt from an active
router in one of the technical
workshops that we offer. In this output
you see the list of prefixes that have
been learned, the IP addresses of the Next
Hop of the routers these will learn from
and various other BGP attributes like
metric, local preference, weight and
path which we will cover going forwards
in this series.
The screen shows you the IPv4 version
and IPv6 version has similar information
but of course for IPv6 adjacencies
and IPv6 network entries.
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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