As we discussed in last post about BSR in PIM sparse mode, Let’s see more detail about BSR in this section...
BSR
is standard protocol, which work with PIM to advertise RP in network.
But we need to elect BSR first. We can define BSR as -BSR is Router,
Which will collect all RP advertisement from network and make a set of
RP address and advertise/share in network. In Cisco Auto-RP - it is
different, Auto-RP will select the best RP and advertise only one best
RP in all network.
Both protocols use the same information which is coming from rp candidate advertisement.
Let me explain this process- First you will select a router. Which you want to designate as BSR
Syntax – ip pim bsr- candidate fastethernet0
Using
this command we can designate the router as BSR router in network. Then
those routers which are near to source or concern router we want to
designate as RP. We need to configure this command.
Syntax- ip pim rp-candidate fastethernet0
At
this time, router will start sending candidate RP announcements to BSR
Routers. BSR will collect the announcements and make a set of all RP
announcements and advertise in network through PIM messages.
BSR advertisement will go thru RPF check same like PIM. Then all
routers will have BSR information in network along with RP information.
As the join request will come to router, Router will check the RP
address and reach to source. BSR is reducing manual overhead to configure static RP in every router.
We can configure redundant BSR in network. In that case we
need to configure priority for BSR. Highest priority will win and
elected as Master BSR. As you enable a router as BSR, it will send
bootstrap messages in network.BSR message contains BSR address with
priority. As other router will receive the bootstrap messages it will
come to know that one more BSR router is in network. It will check the
priority associated with message and select our role. Depending on
priority master will be elected. Higher wins...
Syntax – ip pim bsr-candidate interface [hash-mask-length [priority]]
Priority – 0 to 255
In Maipu Routers - By default, hash-mask-length is 10 and priority is 0.
In Cisco Routers – by default the priority is 0.
In RP also we can configure priority,
In RP lowest priority wins. As we require RP for particular group that
time we can configure Access-list and bind it with RP and advertise with
priority. In case of lower priority BSR will consider that RP and
advertise in network.
Default RP priority in Maipu Router – 192
Default RP priority in Cisco - 0 which specifies 192.
If some RP is advertising lowest priority like
190, then it will master RP which BSR will be advertise in network.
RP send unicast messages to configured BSR
routers continuously. So as the RP change happen in network. It will get
notified by BSR immediately.
Hope
this post clarified you about BSR and RP election and working flow. We
will see configuration and scenario for more understanding in coming
posts...
If you like this post and for any queries Plz comment with your mail id...
