PBR & RSRB

Answered Question
Dec 5th, 2007
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hello


i have a router with one LAN interface and 2 wan interfaces connected to 2 internet ISP.


if i need to let some users go to internet via the first wan interface and some others via the second wan interface, normally i should use policy based routing (PBR)

-if i need automatic failure backup, i think i should use Reliable Static Routing Backup.


but if i need both! some users connect to one ISP and some others to the second and if one link fail all users switch to the functionning link, so how can we combine PBR and reliable static routing backup?

Correct Answer by mheusing about 9 years 5 months ago

Hi,


If you are using PBR and set a next hop f.e. 10.1.1.1 and the next hop is not available, because the interface is down, then normal routing will occur. This likely means in your case, that PBR alone offers the desired behaviour, i.e. send traffic to a specified link, if both interfaces to the two ISPs are available and use the remaining link for all traffic, if one interface fails.


The problem you could encounter is a link failure not being detected. Have a look at "PBR Support for Multiple Tracking Options"

http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a0080457bcc.html

This feature will allow you to use f.e. pings regularly sent by the router to detect a connectivity issue to an ISP and reroute to another path in case no connectivity exists.


Hope this helps! Please rate all posts.


Regards, Martin

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Correct Answer
mheusing Wed, 12/05/2007 - 02:39
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  • Cisco Employee,

Hi,


If you are using PBR and set a next hop f.e. 10.1.1.1 and the next hop is not available, because the interface is down, then normal routing will occur. This likely means in your case, that PBR alone offers the desired behaviour, i.e. send traffic to a specified link, if both interfaces to the two ISPs are available and use the remaining link for all traffic, if one interface fails.


The problem you could encounter is a link failure not being detected. Have a look at "PBR Support for Multiple Tracking Options"

http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a0080457bcc.html

This feature will allow you to use f.e. pings regularly sent by the router to detect a connectivity issue to an ISP and reroute to another path in case no connectivity exists.


Hope this helps! Please rate all posts.


Regards, Martin

ohassairi Thu, 12/06/2007 - 01:56
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thanks for all replies.

but mheusing what is the difference between : (PBR Support for Multiple Tracking Options) and (PBR Recursive Next Hop) .

i find they make the same thing. isn't it?

bvsnarayana03 Thu, 12/06/2007 - 02:19
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To some extent yes they are similar in sending pkts to the next configured hop when previous configured hop is not reachable.


but as the other post mentions, how to track the state of the interface?? There may be errors on link while the interface is still UP. In this case PBR with recrsive lookup still fwd pkts to the same hop since the interface is up. In this case PBR with tracking may notice the errors, considers the hop to be faulty & deliver pkts to the other configured hop.


hope that clarifies.



pls rate all helpful posts.

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