From: maureen schaar (maureen.schaar@gmail.com)
Date: Wed Mar 28 2007 - 11:55:15 ART
Question 1: I labbed it up. I am sending icmp echo from host 12.12.5.5
to host 12.12.7.7 with ip precedence set to 3. I am setting the
next-hop for this traffic to 12.3.12.254 (which is different from the
next-hop in the routing table). See results below in this email.
In a response to question 2, the command reference is quite clear on this:
ip route-cache policy
Enables fast-switching for packets that are forwarded using Policy
Based Routing (PBR).
1. If Cisco Express Forwarding (CEF) is already enabled, this command
is not needed because PBR packets are CEF switched by default.
2. Before you can enable fast-switched PBR, PBR itself must be configured.
3. FSPBR supports all of PBR's match commands and most of PBR's set
commands, with the following restrictions:
The set ip default next-hop and set default interface commands are
not supported.
The set interface command is supported only over point-to-point
links, unless a route cache entry exists using the same interface
specified in the set interface command in the route map.
Also, at the process level, the routing table is consulted to
determine if the interface is on a reasonable path to the destination.
During fast switching, the software does not make this check. Instead,
if the packet matches, the software blindly forwards the packet to the
specified interface.
*** Test results
W2R4#sir 12.12.7.7
Routing entry for 12.12.7.7/32
Known via "ospf 1", distance 110, metric 3, type inter area
Last update from 12.12.48.8 on FastEthernet0/1, 05:16:40 ago
Routing Descriptor Blocks:
* 12.12.48.8, from 12.12.8.8, 05:16:40 ago, via FastEthernet0/1
Route metric is 3, traffic share count is 1
W2R4#sh ip policy
Interface Route map
Serial0/0 PBR
W2R4#
W2R4#sh route-map PBR
route-map PBR, permit, sequence 10
Match clauses:
ip address (access-lists): PBR
Set clauses:
ip next-hop 12.3.12.254
Policy routing matches: 20 packets, 2080 bytes
W2R4#
W2R4#sh access-lists PBR
Extended IP access list PBR
10 permit icmp host 12.12.5.5 host 12.12.7.7 precedence flash (36 matches)
!
interface Serial0/0
ip address 12.12.45.4 255.255.255.0
encapsulation frame-relay
no ip route-cache cef
no ip route-cache
ip policy route-map PBR
frame-relay map ip 12.12.45.4 405
frame-relay map ip 12.12.45.5 405 broadcast
no frame-relay inverse-arp
end
W2R4#deb ip policy
*Mar 28 16:40:32.109: IP: s=12.12.5.5 (Serial0/0), d=12.12.7.7, len
100, policy match
*Mar 28 16:40:32.113: IP: route map PBR, item 10, permit
*Mar 28 16:40:32.113: IP: s=12.12.5.5 (Serial0/0), d=12.12.7.7
(FastEthernet0/0), len 100, policy routed
*Mar 28 16:40:32.113: IP: Serial0/0 to FastEthernet0/0 12.3.12.254
W2R4#ct
Enter configuration commands, one per line. End with CNTL/Z.
W2R4(config)#int se 0/0
W2R4(config-if)#ip route-c policy
W2R4(config-if)#ip route-c cef
W2R4(config-if)#do sr int se 0/0
Building configuration...
Current configuration : 247 bytes
!
interface Serial0/0
ip address 12.12.45.4 255.255.255.0
encapsulation frame-relay
ip route-cache policy
ip policy route-map PBR
frame-relay map ip 12.12.45.4 405
frame-relay map ip 12.12.45.5 405 broadcast
no fram
W2R4(config-if)#
*Mar 28 16:42:08.077: IP: s=12.12.5.5 (Serial0/0), d=12.12.7.7, len
100, policy match
*Mar 28 16:42:08.077: IP: route map PBR, item 10, permit
*Mar 28 16:42:08.077: IP: s=12.12.5.5 (Serial0/0), d=12.12.7.7
(FastEthernet0/0), len 100, policy routed
*Mar 28 16:42:08.077: IP: Serial0/0 to FastEthernet0/0 12.3.12.254
W2R4(config-if)#
So yes, it works nicely with 'ip route-cache policy'.
Maureen
On 3/28/07, iyux2000@gmail.com <iyux2000@gmail.com> wrote:
> Hi, group
> Recently i 'am working on a lab senario about PBR. During my testing, i found the following two questions:
> 1. can we match both "ip precedece value" and "access-list" entries in route-map and set ip next-hop ?
> 2. I know PBR supports fast-switching. Do we need to disable "ip route-cache cef" on the interface that configured PBR ?
>
> For question1, can we use other ways to achieve the same result?
> For example, all traffic with precedence 3 coming from vlan 10 are forwarded to 192.168.0.4 (the next hop). I initially want to use policy-map instead, but i finally found that policy-map cannot support next-hop feature.
>
> Is there some other ways by doing this question?
>
> Thank you for your reply.
>
> Have a lovely day.
>
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