policy based routing

[jonk34567]

what is the diffrence between policy based routing and route filtering

[Leo Laohoo]

Stop spamming the forum with single-topic threads.  Put all your questions in one big thread. 

Specify the purpose of the questions if they are for school work or otherwise.  The reason behind this are two-folds: 

1.  A professor or instructor can tell if the answer is copied somewhere and may he/she might find ways to verify if you are a "hidden genius" or a plagerist. 

2.  What happens in the "wild" and what happens behind text books are two different things:  Text books might give you what happens in an "ideal world" and this is what the instructor wants.  If he/she finds answers that do not comply with text book materials one might not like the grades handed back.

[Joseph W. Doherty]

PBR makes a routing decision based on some policy, rather than just destination address.

For example, if might route packets based on what their source IP is or what kind of traffic or ToS the packet contains.

Route filtering passes route information, not normal traffic, through some kind of filter.  For example, with BGP I might reject sending or receiving routes whose AS path is more than two hops.  Route filters don't have to block, them might also add or amend route information.  For example, as RIP routes are redistributed into OSFP a route tag might be added (to allow such routes to be easily [and later] filtered out of the OSPF route table).

[Julio E. Moisa]

Hi 

I think the other members are provided good explanations about the question, I would like to add other explanation:

PBR can be used for many requests: 

- Traffic manipulation
- Set metrics, communities, etc
- Match prefixes, ACLs

PBR is used commonly with 2 features: match and set.

Router(config)#route-map TEST permit 5
Router(config-route-map)#?
Route Map configuration commands:
continue Continue on a different entry within the route-map
default Set a command to its defaults
description Route-map comment
exit Exit from route-map configuration mode
help Description of the interactive help system
match Match values from routing table
no Negate a command or set its defaults
set Set values in destination routing protocol

Match is used to match any information related to ACL, prefix list, community, metric, etc. 

Router(config-route-map)#
Router(config-route-map)#match ?
additional-paths 
as-path 
clns 
community 
extcommunity 
interface
ip 
ipv6 
length 
local-preference 
mdt-group
metric 
mpls-label 
policy-list 
route-type 
rpki 
source-protocol 
tag 

Set is used to apply one of the following arguments to the matching.

Router(config-route-map)#set ?
as-path Prepend string for a BGP AS-path attribute
automatic-tag Automatically compute TAG value
clns OSI summary address
comm-list set BGP community list (for deletion)
community BGP community attribute
dampening Set BGP route flap dampening parameters
default Set default information
extcomm-list Set BGP/VPN extended community list (for deletion)
extcommunity BGP extended community attribute
global Set to global routing table
interface Output interface
ip IP specific information
ipv6 IPv6 specific information
level Where to import route
local-preference BGP local preference path attribute
metric Metric value for destination routing protocol
metric-type Type of metric for destination routing protocol
mpls-label Set MPLS label for prefix
origin BGP origin code
tag Tag value for destination routing protocol
traffic-index BGP traffic classification number for accounting
vrf Define VRF name
weight BGP weight for routing table

You can include many matches and in some situations you can include many "set".

The PBR uses sequence numbers to be verified, take in consideration that PBR has an implicit deny at the end when there are not matches. In order to avoid any impact you can set up an empty sequence at the end.

The PBR can be applied locally using ip local policy , under the interfaces or under routing protocols like BGP. 

Router filtering is used to allow or block prefixes into a routing protocol, for example:
distribute-lists + other arguments like:

Router(config)#router eigrp 1
Router(config-router)#distri
Router(config-router)#distribute-list ?
<1-199> IP access list number
<1300-2699> IP expanded access list number
WORD Access-list name
gateway Filtering incoming address updates based on gateway
prefix Filter prefixes in address updates
route-map Filter prefixes based on the route-map

Hope this information is useful

:-)