Contents
Why is route filtering used?
Route filtering is a method for selectively identifying routes that are advertised or received from neighbor routers. Route filtering may be used to manipulate traffic flows, reduce memory utilization, or to improve security. For example, it is common for ISPs to deploy route filters on BGP peerings to customers.
What is route filtering in OSPF?
Filter a route coming in from another autonomous system, as part of a redistribution configuration. Filter a route between areas, using a filter list. Filter a route from being installed in an single router’s IP routing table, using a distribute list.
What is route manipulation?
This section covers PBR, route summarization, and route redistribution. You can use PBR to modify the next hop of packets from what is selected by the routing protocol. PBR is useful when the traffic engineering of paths is required.
What is BGP filtering?
BGP filtering is used to control prefixes that are received and advertised to BGP peers. Prefixes exchanged between BGP peers should be controlled with inbound and outbound filters that can match on IP prefixes, AS paths or any other attributes of a BGP prefix (e.g. BGP communities).
Can you filter OSPF routes?
The most basic filter is the inbound distribute-list. The outbound distribute-list is exclusively used to filter OSPF routes in route redistribution between OSPF and a different routing protocol or OSPF process. The distribute-list in can be applied to any router within the area.
How do I filter a route in BGP?
Route filtering is the basis by which Border Gateway Protocol (BGP) policies are set. There are number of ways to filter one or more networks from a BGP peer, including Network Layer Reachability Information (NLRI) and AS_Path and Community attributes. This document discusses filtering based on NLRI only.
What is stubby area in OSPF?
A stub area is an area in which you do not allow advertisements of external routes, which thus reduces the size of the database even more. Instead, a default summary route (0.0. Stub areas are shielded from external routes but receive information about networks that belong to other areas of the same OSPF domain.
What is summarization in OSPF?
A key feature of the OSPF protocol is the ability to summarize routes at area and autonomous system boundaries. Route summarization is important because it reduces the amount of the OSPF LSA flooding and the sizes of LSDBs and routing tables, which also reduces the memory and the CPU utilization on the routers.
How do I filter incoming BGP routes?
You can combine route maps with prefix lists to filter the routes advertised to or received from a BGP peer, to control routes redistributed into BGP, and to set BGP attributes for specific routes. Prefix lists alone can be applied to a neighbor to filter route updates.
How do you influence BGP routes?
To influence the inbound traffic path, customers can use certain attributes (such as MED, AS-PATH, BGP communities) in the updates sent to their providers. Another method is based on the longest prefix-matching behavior and can be accomplished by the BGP conditional route injection.
What port is BGP?
port 179
BGP peers are established by manual configuration between routing devices to create a TCP session on port 179. A BGP-enabled device periodically sends keepalive messages to maintain the connection. Over time, BGP has become the dominant interdomain routing protocol on the Internet.
How do I filter BGP routes?
How is a filter applied in route filtering?
In input filtering, a filter is applied to routes as they are learned from a neighbour. A route that has been filtered out is discarded straight away, and hence not considered for inclusion into the local routing database.
How is route filtering used in BGP peering?
Route Filtering and Manipulation Route filtering is a method for selectively identifying routes that are advertised or received from neighbor routers. Route filtering may be used to manipulate traffic flows, reduce memory utilization, or to improve security. For example, it is common for ISPs to deploy route filters on BGP peerings to customers.
How to configure route filters for Microsoft peering?
Get BGP community values. Create route filter and filter rule. Associate route filter to an ExpressRoute circuit. When Microsoft peering gets configured on your ExpressRoute circuit, the Microsoft edge routers establish a pair of BGP sessions with your edge routers through your connectivity provider. No routes are advertised to your network.
When to use a filter in output filtering?
Output filtering. In output filtering, a filter is applied to routes before they are announced to a neighbour. A route that has been filtered out is never learned by a neighbour, and hence not considered for inclusion in the remote route database.