Policy-Based Routing (Pbr); Configuration Considerations - Dell PowerConnect B-RX Configuration Manual

Policy-Based Routing

Policy-Based Routing (PBR)

Policy-Based Routing (PBR) allows you to use ACLs and route maps to selectively modify and route
IP packets in hardware. The ACLs classify the traffic. Route maps that match on the ACLs set
routing attributes for the traffic.
A PBR policy specifies the next hop for traffic that matches the policy. Using standard ACLs with
PBR, you can route IP packets based on their source IP address. With extended ACLs, you can
route IP packets based on all of the clauses in the extended ACL.
You can configure the device to perform the following types of PBR based on a packet's Layer 3 and
Layer 4 information:
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When a PBR policy has multiple next hops to a destination, PBR selects the first live next hop
specified in the policy that is up. If none of the policy's direct routes or next hops are available, the
packet is routed in the normal way.

Configuration considerations

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BigIron RX Series Configuration Guide
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Select the next-hop gateway.
Send the packet to the null interface (null0).
A PBR policy on an interface takes precedence over a global PBR policy.
You cannot apply PBR on a port if that port already has ACLs, ACL-based rate limiting, or
TOS-based QoS.
The number of route maps that you can define is limited by the system memory. When a route
map is used in a PBR policy, the PBR policy uses up to 6 instances of a route map, up to 6 ACLs
in a matching policy of each route map instance, and up to 6 next hops in a set policy of each
route map instance.
ACLs with the log option configured should not be used for PBR purposes.
PBR ignores explicit or implicit deny ip any any ACL entries, to ensure that for route maps that
use multiple ACLs, the traffic is compared to all the ACLs. PBR also ignores any deny clauses in
an ACL. Traffic that matches a deny clause is routed normally using Layer 3 paths.
PBR always selects the first next hop from the next hop list that is up. If a PBR policy's next hop
goes down, the policy uses another next hop if available. If no next hops are available, the
device routes the traffic in the normal way.
PBR is not supported for fragmented packets. If the PBR's ACL filters on Layer 4 information
like TCP/UDP ports, fragmented packed are routed normally.
You can change route maps or ACL definitions dynamically and do not need to rebind the PBR
policy to an interface.
The CAM can hold up to 1024 ACL, PBR, and Rate Limiting entries and this maximum is divided
as follows:
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