3Com Router User Manual

							BGP Configuration Example477
[RouterD-ospf] network 4.0.0.0 0.0.0.255 area 0
[RouterD] bgp 200
[RouterD-bgp] undo synchronization
[RouterD-bgp] peer 194.1.1.2 as-number 100
[RouterD-bgp] peer 194.1.1.2 as-number 200
To make the configuration effective, use the reset bgp all command to reset all 
BGP neighbors. 
						

							478CHAPTER 30: CONFIGURING BGP 
						

							31
CONFIGURING IP ROUTING POLICY
This chapter covers the following topics:
■IP Routing Policy Overview
■Configure IP Routing Policy
■Displaying and Debugging IP Routing Policy
■Configuring IP Routing Policy
■Troubleshooting IP Routing Policy
IP Routing Policy 
OverviewDuring the information exchange with a peer router, the routing protocol may 
need to receive or distribute only part of the route information that complies with 
specific conditions; and to import only part of the route information learned by 
other protocols that satisfy the preset conditions. In addition, some attributes of 
the imported route information are set in order to satisfy the requirements of the 
protocol. The route strategy also provides measures for the routing protocol to 
implement these functions.
The route strategy consists of a series of rules, classified into three types and used 
for route information filtering in route advertisement, route receiving, and route 
import. Since defining a strategy is similar to defining a group of filters that are 
used during receiving or advertising route information or before the route 
information exchange between different protocols, route strategy is also called 
route filtering.
A common filter is the basis for route strategy implementation. The user defines 
some matching conditions as necessary, which are referred to when making the 
routing strategies. Apply these conditions to different objects such as the 
destination address of the routing information, and the router address publishing 
the routing information, to implement route information filtering.
A routing strategy provides five filters: 
1Routing policy
2Access list
3Aspath-list
4Community-list 
5Prefix-list
These filters serve as the reference for the protocols to work out routing strategies. 
						

							480CHAPTER 31: CONFIGURING IP ROUTING POLICY
Routing PolicyA routing policy matches attributes of the given routing information and sets 
some attributes of the routing information when the conditions are matched. A 
routing policy contains several if-match clauses and apply clauses. The 
if-match clauses specify the matching conditions. The apply clauses specify 
the configuration commands that are executed when the filtering conditions 
specified by if-match clauses are satisfied.
Access ListAn access list can be divided into a standard access list and an extended access list. 
The standard access list is usually used for filtering routing information. When you 
define an access list, you need to specify the network segment range of an IP 
address, to match the destination network segment address or next hop address 
of the routing information and to filter the routing information not satisfying the 
conditions. If an extended access list is used, only the source address matching 
field is used to match the destination network segment of the routing 
information, while the IP address range used to match packet destination address 
specified in the extended access list should be ignored. 
Prefix-listPrefix-list functions are similar to the functions of an access list, which may not be 
easily understood when used for routing information filtering, because it is in the 
format of packet filtering. 
ip ip-prefix is more flexible and comprehensible. 
When applied to routing information filtering, its matching object is the 
destination address information of the routing information. It can also be directly 
used to the router object (gateway), so that the local routing protocol can only 
receive the routing information distributed by specific routers. The addresses of 
these filters must be filtered by prefix-list. In this case, the matching object of 
ip 
ip-prefix
 is the source address of the IP header of the route packet.       
A prefix-list is identified with the list name and consists of several parts, with 
sequence-number specifying the matching order of these parts. In each part, you 
can specify a matching range in the form of the network prefix. Different parts of 
different sequence-numbers are matched using Boolean “OR” operations. When 
the routing information matches a specific part of prefix-list, it is considered 
successfully filtered through the prefix-list.
Aspath-listAspath-list is only used for the BGP protocol. There is an aspath field in the routing 
information packet of the BGP protocol. When the BGP protocol operates with the 
switching routing information, the path of the routing information crossing the AS 
is recorded in this field. Aspath-list is identified with aspath-list-number. When 
defining aspath-list, you can specify an aspath regular expression to match the 
aspath field in the routing information. You can use aspath-list to match the 
aspath field in the BGP routing information, and filter information that does not 
satisfy the conditions. Each list number can be defined with multiple aspath-lists, 
because one list number represents a group of aspath-lists. The matching process 
for acl-numbers uses Boolean “OR” operations, so a match with any one of the list 
is considered successful filtering of the routing information through the aspath list 
identified with this list number. 
The definition of access-path-list is implemented in the BGP configuration. See the 
description of the 
ip as-path acl command in “Define an AS Path-list entry”.
Community-listCommunity-list is only used for the BGP protocol. In the routing information 
packet of the BGP protocol, there is a community attribute field, used to identify a  
						

							Configure IP Routing Policy481
community. Actually, it is a method of grouping according to the destination 
address where the packets are sent. After grouping, the whole group of routing 
information should be distributed, received or imported. The community-list is an 
access list based on community information, used for the BGP protocol. Its 
matching object is the community field of BGP routing information.
Community-list definition is already implemented in BGP configuration. See the 
description of the 
ip community-list command in “Configuring a BGP 
Community”.
Configure IP Routing 
PolicyConfiguring an IP routing policy includes tasks that are described in the following 
sections:
■Defining a Routing Policy
■Define a Matching Rules
■Defining an Apply Clause
■Configuring Route Import
■Defining an IP Prefix List
■Configuring Route Filter
Defining a Routing 
Polic
y
A routing policy consists of several parts and each part has its own if-match 
clauses and applies clauses, with sequence-number specifying the matching order 
of these parts.
Perform the following configurations in system view.
Ta b l e 560   Define a Routing Policy
By default, no routing policy is defined.
permit specifies the matching mode of the defined routing policy node as permit 
mode. When the route item satisfies all if-match clauses of the node, it is 
permitted to pass the filtering of this node and execute apply clauses of this node. 
If the route item does not satisfy the if-match clauses of this node, the next node 
of this routing policy is tested.
deny specifies the matching mode of the defined routing policy node as deny 
mode. When the route item satisfies all if-match clauses of this node, it is rejected 
and the next node is nottested. 
Please note that the parts of different seq-number use Boolean “OR” operations. 
Namely, route information matches every part in turn. Through a certain part of 
routing policy defines filtering through this routing policy.
OperationCommand
Define a routing policy and enter into the 
routing policy view.route-policy policy-name { permit | 
deny } { seq-number }
Delete a routing policyundo route-policy policy-name [ 
permit | deny ] [seq-number ] 
						

							482CHAPTER 31: CONFIGURING IP ROUTING POLICY
Define a Matching RulesThe if-match clause defines matching rules to meet the filtering conditions of the 
routing information of the current routing policy. The matched objects are the 
attributes of this routing information.
Perform the following configurations in routing policy view.
Ta b l e 561   Configure a Matching Rules
By default, AS regular expression, community list, interface type, IP address range, 
metric value, OSPF tag field and OSPF routing information type are not matched.
Note that:
■For one routing policy node, the if-match clauses of the same part use Boolean 
“AND” operations in the matching process so the routing information cannot 
OperationCommand
Specify the AS number to be matched at 
the beginning of the AS path in the 
route-policy.if-match as-path aspath-list-number
Remove the AS number to be matched 
from the beginning of the AS path in the 
route-policy.undo if-match as-path
Specify the BGP community attributes to 
be matched in the route-policy.if-match community-list 
{standard-community-list-number [ 
exact-match ] | 
extended-community-list-number }
Remove the BGP community attributes to 
be matched from the route-policy.undo if-match community-list
Specify the ACL and prefix list to be 
matched in the route-policy.if-match ip address  { acl-number | 
ip-prefix prefix-list-name }
Remove the ACL and prefix list to be 
matched from the route-policy. undo if-match ip address  [ ip-prefix 
]
Specify the interface to be matched in the 
route-policy.if-match interface [ type number ]
Remove the interface to be matched from 
the route-policy. undo if-match interface
Specify the route-policy-matching 
next-hop of the routing information.if-match ip next-hop { acl-number | 
ip-prefix prefix-list-name }
Remove the route-policy-matching 
next-hop of the routing information. undo if-match ip next-hop [ ip-prefix 
]
Specify the cost of the routing information 
to be matched in the route-policy. if-match cost cost 
Remove the cost of the routing 
information to be matched in the 
route-policyundo if-match cost
Specify the tag of OSPF routing 
information to be matched in the 
route-policy.if-match tag tag-value
Delete the tag of OSPF routing 
information to be matched in the 
route-policy.undo if-match tag 
Specify the matched OSPF route type (i.e. 
internal or external) in the routing policy. if-match route-type { internal | 
external }
Delete the matched OSPF route type in the 
routing policyundo if-match route-type 
						

							Configure IP Routing Policy483
be filtered through the routing policy unless it matches all if-match clauses of 
this part and it can execute the operation of teh apply sub-clause.
■If an if-match clause is not specified, all routing information is filtered through 
the policy of this node.
Defining an Apply 
ClauseThe apply clause specifies the configuration commands that are executed after 
the filtering conditions specified by the 
if-match clause are satisfied. The 
commands are used to modify attributes of the routing information.
Perform the following configurations in Routing policy view.
Ta b l e 562   Define a Setting Clause
By default, AS number, BGP community attribute, next hop, local preference, 
metric value, origin attribute and routing information tag field are not set.
Configuring Route 
ImportDifferent routing protocols can import and share the routing information. When 
the routing information of other protocols is imported, the inappropriate routing 
information can be filtered The metric of distributed destination routing protocol 
cannot exchange with that of the imported original routing protocol. At this time, 
a route metric should be specified for the imported route.
Perform the following configurations in RIP view, OSPF view, or BGP view.
OperationCommand
Specify the AS number ahead of the 
original AS path in Routing policy. apply as-path aspath-list-number
Cancel the AS number ahead of the 
original AS path in Routing policy. undo apply as-path
Set BGP community attribute in Routing 
policy apply community { { aa:nn | 
no-export-subconfed | no-advertise | 
no-export } [ addtive ] |  none }
Cancel BGP community attribute in 
Routing policyundo apply community
Set the next hop address of BGP routing 
information. apply ip next-hop ip-address
Cancel the next hop address of BGP 
routing information. undo apply ip next-hop
Set the local preference of BGP routing 
information. apply local-preference value
Cancel the local preference of BGP routing 
information. undo apply local-preference
Set the cost of routing information. apply cost cost
Cancel the cost of routing information. undo apply cost
Set the origin attribute of the original 
route in the Route-policy apply origin { igp | egp as-number | 
incomplete }
Remove the origin attribute of the original 
route in the Route-policy. undo apply origin
Set the OSPF tag value apply tag tag-value
Cancel the OSPF tag value undo apply tag  
						

							484CHAPTER 31: CONFIGURING IP ROUTING POLICY
Ta b l e 563   Configure Route Import
By default, a protocol does not import routes from other domains into the its 
routing table.
protocol specifies the source routing domain that can be imported. At present, it 
can import routes domain such as direct, static, RIP, OSPF, OSPF-ASE and BGP.
Software supports importing route information found by the ollowing protocols 
into the route table:
■direct: network segment (or host) route directly connected to the routers 
interface
■static: static route
■RIP: routes discovered by rip
■OSPF: routes discovered by ospf
■OSPF-ASE: external routes discovered by ospf
■BGP: routes discovered by bgp
med med or cost cost: specifies the metric value of the imported routes.
bandwidth is the route bandwidth, ranging from 1 to 4294967295 kbyte/s.
delay is the route time delay, each unit stands for 10µs, ranging from 1 to 
16777215
reliability is the channel reliability, ranging 0 to 255. 255 stands for 100% 
creditable.
loading is the channel seizure rate, ranging 1 to 255, 255 stands for 100% seized.
mtu is the maximum transfer unit of route, ranging from 1 to 65535 byte.
route-policy policy-name specifies imported routes which matches the 
specified routing policy name. This item can be used in the routing protocol 
configuration except in the OSPF view.
tag tag-value sets the tag value of the imported route when ospf is importing 
other protocol routes.
OperationCommand
Configure route import in RIPimport-route protocol [ cost cost ] [ 
route-policy route-policy-name ]
Cancel route importundo import-route protocol
Configure route import in OSPFimport-route protocol [ cost cost ] [ 
type 1 | 2 ] [ tag tag-value ]
Cancel route importundo import-route protocol [ cost 
cost ] [ type 1 | 2 ] [ tag tag-value 
]
Configure route import in BGPimport-route protocol [ med med ] [ 
tag tag-value ] [ type 1 | 2 ] [ 
route-policy policy-name ]
Cancel route importundo import-route protocol 
						

							Configure IP Routing Policy485
type is the type of ospf external route corresponding to the imported route when 
ospf is importing other protocol routes. 
type 1 refers to external route type 1 and 
type 2 refers to external route type 2.
The metric value of the imported route can be set as the following:
1Specify the metric value with the apply cost command.
2Filter the route with routing policy and set attributes for the route matching the 
conditions.
3If neither of the above is specified, the imported route uses the default metric 
value. The default metric can be specified with the 
default-med command.
When both routing policy and med value are specified, the routing information 
matching the routing policy will use the metric specified by the 
apply command 
of a routing policy.
Defining an IP Prefix ListAn IP prefix list is identified with the list name and consists of several parts, with 
the sequence-number specifying the matching order of these parts. In each part, 
you can specify an individual matching range in the form of network prefix.
It should be noted that:
■In the process of matching, different parts of different sequence-numbers use 
Boolean “OR” operations and the routing information matches different parts 
in turn. Matched with a specific part of the IP prefix list is considered as 
successfully filter through this IP prefix list 
Perform the following configurations in system view.
Ta b l e 564   Define an IP Prefix List
By default, no IP prefix list is defined.
Configuring Route FilterIn some cases, only the routing information that meets the condition should be 
distributed or imported, to prevent the neighboring routers from receiving private 
information of other routes. A prefix-list or access list in the route strategy is used 
to filter the routing information.
Perform the following configurations in RIP view, OSPF view, or BGP view.
1Configure filtering route information received
Define a strategic rule and quote an ACL or prefix-list to filter the routing 
information that does not meet the requirements when receiving routes. Specify 
an IP prefix list through gateway keywords, filtering the address of the 
information router to receive only the updating messages from specific 
neighboring routers.
OperationCommand
Define an IP prefix listip ip-prefix  prefix-list-name [ 
index index-number ] { permit | deny 
} network/len [ greater-equal 
ge-value ] [ less-equal le-value ]
Cancel an IP prefix list undo ip ip-prefix prefix-list-name [ 
index seq-number ] [ permit | deny ] 
						

							486CHAPTER 31: CONFIGURING IP ROUTING POLICY
Ta b l e 565   Configure Filtering Route Information Received
2Configure filtering the route information being advertised
Define a strategic rule and quote an ACL or prefix-list to filter the routing 
information that does not meet the requirements when receiving routes. Specify 
the protocol to filter only the distributed protocol routing information.
Ta b l e 566   Configure Filtering RouteInformation Being Advertised
By default, no route information received or being advertised is filtered.
protocol specifies the routing domain that can will be filtered. At present, it can 
filter routes domain as follows:
■direct: the network segment (host) route directly connected with the local 
interface.
■static: static route
■RIP: route discovered by RIP protocol+
■OSPF: route discovered by OSPF protocol
■OSPF-ASE: external route discovered by OSPF protocol
■BGP: route discovered by BGP protocol
Displaying and 
Debugging IP Routing 
PolicyPerform the following configurations in all views.
OperationCommand
Filter the route information received from 
a specified gateway filter-policy gateway 
prefix-list-name import
Change or cancel filtering the route 
information received from a specified 
gatewayundo filter-policy gateway 
prefix-list-name import
Filter the route information receivedfilter-policy {acl-number | 
ip-prefix prefix-list-name } import
Change or cancel filtering route 
information receivedundo filter-policy {acl-number | 
ip-prefix prefix-list-name } import
Filter routing information received from a 
specified gateway and the routing 
information received according to 
prefix-listfilter-policy ip-prefix 
prefix-list-name gateway 
prefix-list-name import
Change or cancel filtering the routing 
information received from a specified 
gateway and the routing information 
received according to prefix-listundo filter-policy ip-prefix 
prefix-list-name gateway 
prefix-list-name import
OperationCommand
Filter the route information being 
advertisedfilter-policy {acl-number | 
ip-prefix prefix-list-name } export [ 
protocol ]
Change or cancel filtering route 
information being advertisedundo filter-policy { acl-number | 
ip-prefix prefix-list-name } export [ 
protocol ]