3Com Router User Manual

							Configuring BGP 467
Ta b l e 551   Allow the Import of Network 0.0.0.0 into the BGP
By default, the import of network 0.0.0.0 into BGP is disabled.
Defining an Access List 
Entry, an AS Path-list 
Entry, a Routing PolicyThis section describes the configuration of an access list, an AS path list, and a 
routing policy.
Define an access list entry
See “Access Control List” in ****need proper ref here 3Com Router Operation 
Manual (Security Configuration)******. for more details.
Define an AS Path-list entry
There is an AS path 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 used to match the aspath field in the routing 
information. Use 
aspath-list to match the aspath field in the BGP routing 
information, filtering the information that does not meet the conditions. You can 
define multiple aspath-lists for one list number so that one list number represents 
a group of aspath-lists. Each AS path list is identified with numbers.
Perform the following configurations in system view.
Ta b l e 552   Define a BGP-related ACL Entry
By default, no access list entry is defined.
In the matching process, many aspath-list-number us Boolean “OR” operation so 
that if the routing information passes one item, information is filtered by the 
as-path list identified with this list number.
Define a routing policy
A routing policy is an important way for BGP to implement the route strategy. 
According to the matching result of the route attribute, BGP decides on the 
operations to be applied on a route attribute. In each routing policy, there can be 
several matching rules, labeled with a serial number. When importing a route, it is 
compared to a rule by number, from small to large. When the first matched rule is 
found, the matching process is completed. If no matched rules are found, router 
reception and transmission is canceled.
OperationCommand
Allow the import of network 0.0.0.0 into 
the BGPdefault-information
Disable the import of network 0.0.0.0 into 
the BGPundo default-information
OperationCommand
Define a BGP-related ACL entryip as-path acl aspath-list-number { 
permit | deny } as-regular-expression
Remove a BGP-related ACL entryundo ip as-path acl 
aspath-list-number 
						

							468CHAPTER 30: CONFIGURING BGP
Perform the following configurations in system view.
Ta b l e 553   Define a Routing Policy
Define a match rule
Perform the following configurations in BGP Routing policy view.
Ta b l e 554   Define a Match Rules
By default, AS regular expression, community list, interface type, IP address range, 
and metric value are not matched.
See “Define matching rules” of “Configuration of IP Routing Policy” for details.
Define an apply clause
Perform the following configurations in Routing policy view.
Ta b l e 555   Define An Apply Clause
OperationCommand
Define a routing policy and enter into the 
Routing policy viewroute-policy policy-name { permit | 
deny } [ seq-number ]
Remove a specified routing policyundo route-policy policy-name [ 
permit | deny ] [seq-number ]
OperationCommand
Specify a BGP AS path list to be matched 
in routing policyif-match as-path aspath-list-number
Delete a BGP AS path list to be matched in 
routing policyundo if-match as-path
Specify BGP community list number to be 
matched in routing policy.if-match community 
{standard-community-list-number [ 
exact-match ] | 
extended-community-list-number }
Delete BGP community listundo if-match community
Define the matched routing access control 
list and prefix list in routing policy.if-match ip address  { acl-number | 
ip-prefix prefix-list-name }
Remove a standard access list or a prefix 
listundo if-match ip address  [ ip-prefix 
]
Define matched the type of  interfaceif-match interface [ type number ]
Remove the matched interfaceundo if-match interface
Specify the next hop to be matched in 
Route-policy by an access list or an prefix 
list specifiedif-match ip next-hop { acl-number | 
ip-prefix prefix-list-name }
Remove the destination address of the 
matched routeundo if-match ip next-hop [ ip-prefix 
]
Define matched the specified costif-match cost cost 
Delete the specified costundo if-match cost
OperationCommand
Set the BGP AS path access listapply as-path aspath-list-number
Delete BGP AS-path attribute to BGP 
routesundo apply as-path 
						

							Configuring BGP 469
By default, AS serial number, BGP community attribute, next hop, local preference, 
metric value, and origin attributes are not applied.
See “Define Apply Clause “of “Configuration of IP Routing Policy” for details.
Configuring a Route 
Filter for BGPPerform the following configurations in BGP view.
Configure a route filter for information received by BGP
Ta b l e 556   Filter Routing Information Received from BGP
Set the communities attributesapply community { { [aa:nn ] [ 
no-export-subconfed ] [ no-advertise 
] [ no-export ] } [ additive ] | none 
| additive }
Delete the communities attributesundo apply community
Set the next hop of BGP routing 
informationapply ip next-hop ip-address
delete the next hop of BGP routingundo apply ip next-hop
Set the local preference value of source 
routeapply local-preference value
Cancel the local preference value of 
source route undo apply local-preference
Apply cost to the imported routesapply cost cost
Restore the destination routing protocols 
cost valueundo apply cost
Set the origin attribute of the original 
route in the Route-policyapply origin { igp | egp as-number | 
incomplete }
Remove the origin attributeundo apply origin
Operation Command
OperationCommand
Filter routing information received from a 
specified gatewayfilter-policy gateway 
prefix-list-name import
Change or cancel filtering the routing 
information received from a specified 
gatewayundo filter-policy gateway 
prefix-list-name import
Filter the routing information receivedfilter-policy {acl-number | ip-prefix 
prefix-list-name } import
Change or cancel filtering routing 
information receivedundo filter-policy {acl-number | 
ip-prefix prefix-list-name } import
Configure to filter the routing information 
received from the specified address and 
that matching prefix-list. filter-policy ip-prefix 
prefix-list-name { gateway 
prefix-list-name | import }
Configure not to filter the routing 
information received from the specified 
address and that matching prefix-list. undo filter-policy ip-prefix 
prefix-list-name { gateway 
prefix-list-name | import } 
						

							470CHAPTER 30: CONFIGURING BGP
Configure Filtering Route Information being Advertised by BGP
Ta b l e 557   Filter Routing Information Being Advertised by BGP
By default, BGP does not filter any route information that is received or advertised.
protocol specifies the routing domain that can will be filtered. At present, BGP 
can filter route domains such as connected, static, OSPF and OSPF-ASE.
See “Configure Route Filter” of “Configuration of IP Routing Policy” for details.
Resetting BGP 
ConnectionsAfter modifying a BGP configuration, you must turn off the current BGP 
connections and reset BGP connections to make the new configuration effective.
Perform the following configurations in system view.
Ta b l e 558   Reset BGP Connections
Displaying and 
Debugging BGP Ta b l e 559   Display and Debug BGP
OperationCommand
Filter routing information being advertised 
by BGPfilter-policy {acl-number | 
ip-prefix prefix-list-name } export [ 
protocol ]
Cancel filtering routing information being 
advertised by BGPundo filter-policy {acl-number | 
ip-prefix prefix-list-name } export [ 
protocol ]
OperationCommand
Reset BGP connection reset bgp { all | peer-id }
Clear routing flapping attenuation 
information and cancel the dampening 
over the routes. reset bgp dampening [ network-address 
[ mask ] ]
Reset the BGP connection of a specified 
peer or all members of a peer group reset bgp group group-name 
OperationCommand
Display BGP path information display bgp paths 
as-regular-expression
Display AS filtered path information in 
BGPdisplay ip as-path-acl acl-number
Display the routing information of the 
specified IP address in the routing table.display bgp routing-table ip-address 
[ mask ]
Display CIDR routedisplay bgp routing-table cidr
Display routing information of the 
specified BGP communitydisplay bgp routing-table community [ 
[aa:nn ] [ no-export-subconfed ] [ 
no-advertise] [ no-export ] ] [ 
exact-match ]
Display routing information of permitted 
in the specified BGP community listdisplay bgp routing-table comm-list 
community-list-number [ exact-match]
Display Dampening routedisplay bgp routing-table dampened
Display the route matching the specified 
access listdisplay bgp routing-table acl 
acl-number 
						

							BGP Configuration Example471
BGP Configuration 
ExampleThis section describes several different configurations of BGP with a suggested 
procedure for each configuration.
Configuring the AS 
Confederation AttributeAs shown in the following diagram, AS 100 is divided into 3 sub-ASs: 1001, 1002, 
1003, which are configured with EBGP, confederation EBGP and IBGP.
Display route flap informationdisplay bgp routing-table 
flap-information [ { 
regular-expression 
as-regular-expression } | { acl 
acl-number } | { network-address [ 
mask [ longer-match ] ] } ]
Display the route with inconsistent source 
ASdisplay bgp routing-table 
different-origin-as
Display peer informationdisplay bgp peer [ peer-address ]
Display routing information distributed 
through BGPdisplay bgp routing-table network 
Display peer group informationdisplay bgp group [ group-name ]
–table regular-expressdisplay bgp routing-table 
regular-expression 
as-regular-expression
Display BGP route summary informationdisplay bgp summary
Display the configured routing policy 
informationdisplay route-policy policy-name
Enable BGP packet debugging.debugging bgp { all | event | { 
keepalive | open | packet | update } 
[ receive | send ] [ verbose ] } }
Disable BGP packet debugging undo debugging bgp { all | event | 
keepalive | open | packet | update }
Operation Command 
						

							472CHAPTER 30: CONFIGURING BGP
Figure 154   Networking diagram of configuring AS confederation 
1Configure Router A:
[RouterA] bgp 1001
[RouterA-bgp] undo synchronization
[RouterA-bgp] confederation id 100
[RouterA-bgp] confederation peer-as 1002 1003
[RouterA-bgp] peer 172.68.10.2 as-number 1002
[RouterA-bgp] peer 172.68.10.3 as-number 1003
2Configure Router B:
[RouterB] bgp 1002
[RouterA-bgp] undo synchronization
[RouterB-bgp] confederation id 100
[RouterB-bgp] confederation peer-as 1001 1003
[RouterB-bgp] peer 172.68.10.1 as-number 1001
[RouterB-bgp] peer 172.68.10.3 as-number 1003
3Configure Router C:
[RouterC] bgp 1003
[RouterA-bgp] undo synchronization
[RouterC-bgp] confederation id 100
[RouterC-bgp] confederation peer-as 1001 1002
[RouterC-bgp] peer 172.68.10.1 as-number 1001
[RouterC-bgp] peer 172.68.10.2 as-number 1002
[RouterC-bgp] peer 156.10.1.2 as-number 200
[RouterC-bgp] peer 172.68.1.2 as-number 1003
Configuring BGP Route 
ReflectorRouter B receives a BGP update message and forwards the update to Router C, 
which is configured as a route reflector and has two clients: Router B and Router 
D. When Router C receives routing update from Router B, it reflects the 
information to Router D. Therefore, an IBGP connection is not necessary between 
Router B and Router D, because Router C will reflect the information to Router D.
AS200
AS100
AS1002AS1001
AS1003
Ethernet
172.68.10.1172.68.10.2
172.68.10.3
172.68.1.2 172.68.1.1
156.10.1.1
156.10.1.2Router A
Router B
Router CRouter D
Router E 
						

							BGP Configuration Example473
Figure 155   Networking diagram of configuring route reflector
1Configure Router A:
[RouterA] bgp 100
[RouterA-bgp] undo synchronization
[RouterA-bgp] peer 192.1.1.2 as-number 200
[RouterA-bgp] interface serial 0
[RouterA-Serial0] ip address 192.1.1.1 255.255.255.0
2Configure Router B:
aConfigure BGP peers 
[RouterB] bgp 200
[RouterA-bgp] undo synchronization
[RouterB-bgp] peer 192.1.1.1 as-number 100
[RouterB-bgp] peer 193.1.1.1 as-number 200
bEnable OSPF
[RouterB] ospf enable 
cConfigure Serial 0
[RouterB-ospf] interface serial 0
[RouterB-Serial0] ip address 192.1.1.2 255.255.255.0
dConfigure Serial 1
[RouterB-Serial0] interface serial 1
[RouterB-Serial1] ip address 193.1.1.2 255.255.255.0
[RouterB-Serial1] ospf enable area 0
3Configure Router C:
aConfigure BGP peers and route reflector clients
[RouterC] bgp 200
[RouterA-bgp] undo synchronization
[RouterC-bgp] peer 193.1.1.2 as-number 200 reflect-client
[RouterC-bgp] peer 193.1.1.2 reflect-client
[RouterC-bgp] peer 194.1.1.2 as-number 200 reflect-client
[RouterC-bgp] peer 194.1.1.2 reflect-client
bEnable OSPF
[RouterC] ospf enable 
cConfigure Serial 0
[RouterC-ospf] interface serial 0
IB GPIBGP
EBGP
Route reflector clientRoute reflec tor
S1
 194. 1. 1.1/24 S0
193.1.1. 1/ 24
S1
193.1.1.2/24S0
194.1.1. 2/ 24 S0
192. 1. 1. 2/24
S0
192.1.1.1/242.2.2.2
4. 4. 4.4
1.1. 1. 13.3.3. 3
AS100 AS200
Connected w ith
netw ork 1. 0.0.0
S1Router C
Router B
Router D Router A
Route reflector c lient
Router E
S2
S0IBGP
5.5.5.5 
						

							474CHAPTER 30: CONFIGURING BGP
[RouterC-Serial0] ip address 193.1.1.1 255.255.255.0
dConfigure Serial 1
[RouterC-Serial0] interface serial 1
[RouterC-Serial1] ip address 194.1.1.1 255.255.255.0
[RouterC-Serial1] ospf enable area 0
4Configure Router D:
aConfigure BGP peers 
[RouterD] bgp 200
[RouterA-bgp] undo synchronization
[RouterD-bgp] peer 194.1.1.1 as-number 200 
bEnable OSPF
[RouterD] ospf enable 
cConfigure Serial 0
[RouterD-ospf] interface serial 0
[RouterD-Serial0] ip address 194.1.1.2 255.255.255.0
[RouterD-Serial0] ospf enable area 0
View BGP routing table on Router B with display bgp routing-table 
command. Note that Router B knows that network 1.0.0.0 exists.
[RouterB] display bgp routing-table
View BGP routing table on Router C with display bgp routing-table 
command. Note that Router C knows that network 1.0.0.0 exists.
[RouterD] display bgp routing-table
Configuring BGP Path 
SelectionThis example describes how the administrator manages the routing with the BGP 
attribute. All routers are configured with BGP. OSPF is used by IGP in AS200. 
Router A is in AS100, functioning as the BGP peer of Router B and Router C in 
AS200. When Router B and Router C run IBGP to Router D, Router D is also in 
AS200.
network next hopmetriclocalpref
1.0.0.0192.1.1.10
networknext hop metricllocalpref
1.0.0.0194.1.1.1 0100 
						

							BGP Configuration Example475
Figure 156   Networking diagram of configuring BGP path selection
1Configure Router A:
[RouterA] interface serial 0
[RouterA-Serial0] ip address 192.1.1.1 255.255.255.0
[RouterA] interface serial 1
[RouterA-Serial1] ip address 193.1.1.1 255.255.255.0
[RouterA-Serial1] quit
aStart BGP
[RouterA] bgp 100
[RouterA-bgp] undo synchronization
bSpecify BGP transmission network
[RouterA-bgp] network 1.0.0.0 mask 255.0.0.0
[RouterA-bgp] network 2.0.0.0 mask 255.0.0.0
cConfigure peer
[RouterA-bgp] peer 192.1.1.2 as-number 200
[RouterA-bgp] peer 193.1.1.2 as-number 200
dConfigure MED attribute of Router A
■Add access list to Router A and enable network 1.0.0.0.
[RouterA-bgp] acl 1
[RouterA-acl-1] rule permit source 1.0.0.0 0.255.255.255
■Define two routing diagram, namely set_med_50 and set_med_100. The first 
routing diagram is network 1.0.0.0. The MED attribute is 50, and the second 
MED attribute is 100.
[RouterA-acl-1] route-policy set_med_50 permit 1
[RouterA-route-policy] if-match ip address  1
[RouterA-route-policy] apply cost 50
[RouterA-route-policy] quit
[RouterA] route-policy set_med_100 permit 1
[RouterA-route-policy] if-match ip address  1
■[RouterA-route-policy] apply cost 100Apply the routing diagram set_med_50 
to the exit routing update of Router C (193.1.1.2). Apply the routing diagram 
set_med_100 to exit routing update of Router B (192.1.1.2).
[RouterA] bgp 100
[RouterA-bgp] peer 193.1.1.2 route-policy set_med_50 export
[RouterA-bgp] peer 192.1.1.2 route-policy set_med_100 export
Router B
Router CRouter D
Router A
S0
194.1.1.2/24
S0 192.1.1.1/24
S1 193.1.1.1/24
S0 193.1.1.2/24S1
195.1.1.2/24 S0
192.1.1.2/242.2.2.2
4.4.4.4
3.3.3.3 1.1.1.1
AS100AS200
S0
194.1.1.1/24
S1
195.1.1.1/24
IBGP IBGP EBGP
EBGP1.0.0.0To network
2.0.0.0
2.0.0.0 To network To network
2.0.0.0 To network 
						

							476CHAPTER 30: CONFIGURING BGP
2Configure Router B:
[RouterB] interface serial 0
[RouterB-Serial0] ip address 192.1.1.2 255.255.255.0
[RouterB] interface serial 1
[RouterB-Serial1] ip address 194.1.1.2 255.255.255.0
[RouterB] ospf enable
[RouterB-ospf] network 194.1.1.0 0.0.0.255 area 0
[RouterB-ospf] network 192.1.1.0 0.0.0.255 area 0
[RouterB] bgp 200
[RouterB-bgp] undo synchronization
[RouterB-bgp] peer 192.1.1.1.1 as-number 100
[RouterB-bgp] peer 194.1.1.1.1 as-number 200
[RouterB-bgp] peer 195.1.1.1.2 as-number 200
3Configure Router C:
[RouterC] interface serial 0
[RouterC -Serial] ip address 193.1.1.2 255.255.255.0
[RouterC] interface serial 1
[RouterC-Serial1] ip address 195.1.1.2 255.255.255.0
[RouterC] ospf enable
[RouterC-ospf] network 193.1.1.0 0.0.0.255 area 0
[RouterC-ospf] network 195.1.1.0 0.0.0.255 area 0
[RouterC] bgp 200
[RouterC-bgp] undo synchronization
[RouterC-bgp] peer 193.1.1.1 as-number 100
[RouterC-bgp] peer 194.1.1.2 as-number 200
[RouterC-bgp] peer 195.1.1.1 as-number 200
Set the local preference attribute of Router C.
■Add access list 1 to Router C and enable network 1.0.0.0.
[RouterC-bgp] acl 1
[RouterC-acl-1] rule permit source 1.0.0.0 0.255.255.255
■Define a routing diagram named localpref. In the diagram, the local preference 
of the route matching access list 1 is set to 200 and the local preference of the 
route not matching access list 1 is 100.
[RouterC-acl-1]route-policy localpref permit 1
[RouterC-route-policy] if-match ip address  1
[RouterC-route-policy] apply local-preference 200
[RouterC-route-policy] route-policy localpref permit 2
[RouterC-route-policy] apply local-preference 100
■Apply this routing diagram to the entry traffic from BGP peer 193.1.1.2 (Router 
A).
[RouterC] bgp200
[RouterC-bgp] peer 193.1.1.1 route-policy localpref import
4Configure Router D:
[RouterD] interface serial 0
[RouterD-Serial0] ip address 194.1.1.1 255.255.255.0
[RouterD] interface serial 1
[RouterD-Serial1] ip address 195.1.1.1 255.255.255.0
[RouterD] ospf enable
[RouterD-ospf]network 194.1.1.0 0.0.0.255 area 0
[RouterD-ospf]network 195.1.1.0 0.0.0.255 area 0