When two BGP-enabled
devices are in the same autonomous system (AS), the BGP session is called
an internal BGP session, or IBGP session. BGP uses the same
message types on IBGP and external BGP (EBGP) sessions, but the rules for when
to send each message and how to interpret each message differ slightly. For
this reason, some people refer to IBGP and EBGP as two separate protocols.
Figure1-8: Internal and External BGP
In Figure 1-8, Device Jackson, Device Memphis, and Device
Biloxi have IBGP peer sessions with each other. Likewise, Device Miami and
Device Atlanta have IBGP peer sessions between each other.
The purpose of IBGP is
to provide a means by which EBGP route advertisements can be forwarded
throughout the network. In theory, to accomplish this task you could
redistribute all of your EBGP routes into an interior gateway protocol (IGP),
such as OSPF or IS-IS. This, however, is not recommended in a production
environment because of the large number of EBGP routes in the Internet and
because of the way that IGPs operate. In short, with that many routes the IGP
churns or crashes.
Generally, the
loopback interface (lo0) is used to establish connections between IBGP peers.
The loopback interface is always up as long as the device is operating. If
there is a route to the loopback address, the IBGP peering session stays up. If
a physical interface address is used instead and that interface goes up and
down, the IBGP peering session also goes up and down. Thus the loopback
interface provides fault tolerance in case the physical interface or the link
goes down, if the device has link redundancy.
While IBGP neighbors
do not need to be directly connected, they do need to be fully meshed. In this
case, fully meshed means that each device is logically connected to every other
device through neighbor peer relationships. The neighbor statement
creates the mesh. Because of the full mesh requirement of IBGP, you must
configure individual peering sessions between all IBGP devices in the AS. The
full mesh need not be physical links. Rather, the configuration on each routing
device must create a full mesh of peer sessions (using multiple neighbor statements).
Configuring Internal BGP
Peering Sessions on Logical Systems
Overview
In
this example, you configure internal BGP (IBGP) peering sessions.
In
the sample network, the devices in AS 17 are fully meshed in the group internal-peers. The devices have
loopback addresses 192.168.6.5, 192.163.6.4, and 192.168.40.4.
Figure 6 shows a typical
network with internal peer sessions.
Figure 6: Typical Network with IBGP Sessions
Configuration
CLI Quick Configuration
To quickly configure
this example, copy the following commands, paste them into a text file, remove
any line breaks, change any details necessary to match your network
configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.
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set logical-systems A
interfaces lt-0/1/0 unit 1 description to-B
set logical-systems A
interfaces lt-0/1/0 unit 1 encapsulation ethernet
set logical-systems A
interfaces lt-0/1/0 unit 1 peer-unit 2
set logical-systems A
interfaces lt-0/1/0 unit 1 family inet address 10.10.10.1/30
set logical-systems A
interfaces lo0 unit 1 family inet address 192.168.6.5/32
set logical-systems A protocols
bgp group internal-peers type internal
set logical-systems A protocols
bgp group internal-peers local-address 192.168.6.5
set logical-systems A protocols
bgp group internal-peers export send-direct
set logical-systems A protocols
bgp group internal-peers neighbor 192.163.6.4
set logical-systems A protocols
bgp group internal-peers neighbor 192.168.40.4
set logical-systems A protocols
ospf area 0.0.0.0 interface lo0.1 passive
set logical-systems A protocols
ospf area 0.0.0.0 interface lt-0/1/0.1
set logical-systems A
policy-options policy-statement send-direct term 2 from protocol direct
set logical-systems A
policy-options policy-statement send-direct term 2 then accept
set logical-systems A routing-options
router-id 192.168.6.5
set logical-systems A
routing-options autonomous-system 17
set logical-systems B
interfaces lt-0/1/0 unit 2 description to-A
set logical-systems B
interfaces lt-0/1/0 unit 2 encapsulation ethernet
set logical-systems B
interfaces lt-0/1/0 unit 2 peer-unit 1
set logical-systems B
interfaces lt-0/1/0 unit 2 family inet address 10.10.10.2/30
set logical-systems B
interfaces lt-0/1/0 unit 5 description to-C
set logical-systems B
interfaces lt-0/1/0 unit 5 encapsulation ethernet
set logical-systems B
interfaces lt-0/1/0 unit 5 peer-unit 6
set logical-systems B
interfaces lt-0/1/0 unit 5 family inet address 10.10.10.5/30
set logical-systems B
interfaces lo0 unit 2 family inet address 192.163.6.4/32
set logical-systems B protocols
bgp group internal-peers type internal
set logical-systems B protocols
bgp group internal-peers local-address 192.163.6.4
set logical-systems B protocols
bgp group internal-peers export send-direct
set logical-systems B protocols
bgp group internal-peers neighbor 192.168.40.4
set logical-systems B protocols
bgp group internal-peers neighbor 192.168.6.5
set logical-systems B protocols
ospf area 0.0.0.0 interface lo0.2 passive
set logical-systems B protocols
ospf area 0.0.0.0 interface lt-0/1/0.2
set logical-systems B protocols
ospf area 0.0.0.0 interface lt-0/1/0.5
set logical-systems B
policy-options policy-statement send-direct term 2 from protocol direct
set logical-systems B
policy-options policy-statement send-direct term 2 then accept
set logical-systems B
routing-options router-id 192.163.6.4
set logical-systems B
routing-options autonomous-system 17
set logical-systems C
interfaces lt-0/1/0 unit 6 description to-B
set logical-systems C
interfaces lt-0/1/0 unit 6 encapsulation ethernet
set logical-systems C
interfaces lt-0/1/0 unit 6 peer-unit 5
set logical-systems C
interfaces lt-0/1/0 unit 6 family inet address 10.10.10.6/30
set logical-systems C
interfaces lo0 unit 3 family inet address 192.168.40.4/32
set logical-systems C protocols
bgp group internal-peers type internal
set logical-systems C protocols
bgp group internal-peers local-address 192.168.40.4
set logical-systems C protocols
bgp group internal-peers export send-direct
set logical-systems C protocols
bgp group internal-peers neighbor 192.163.6.4
set logical-systems C protocols
bgp group internal-peers neighbor 192.168.6.5
set logical-systems C protocols
ospf area 0.0.0.0 interface lo0.3 passive
set logical-systems C protocols
ospf area 0.0.0.0 interface lt-0/1/0.6
set logical-systems C
policy-options policy-statement send-direct term 2 from protocol direct
set logical-systems C
policy-options policy-statement send-direct term 2 then accept
set logical-systems C
routing-options router-id 192.168.40.4
set logical-systems C
routing-options autonomous-system 17
Device
A
Step-by-Step Procedure
The
following example requires you to navigate various levels in the configuration
hierarchy. For information about navigating the CLI, see Using the CLI Editor in
Configuration Mode in the CLI User Guide.
To
configure internal BGP peer sessions on Device A:
- Configure
the interfaces.
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[edit logical-systems A interfaces
lt-0/1/0 unit 1]
user@R1# set
description to-B
user@R1# set
encapsulation ethernet
user@R1# set
peer-unit 2
user@R1# set
family inet address 10.10.10.1/30
user@R1# set
family inet address 192.168.6.5/32
user@R1# up
user@R1# up
[edit logical-systems A interfaces]
user@R1# set
lo0 unit 1 family inet address 192.168.6.5/32
user@R1# exit
[edit]
user@R1# edit
logical-systems B interfaces lt-0/1/0
[edit logical-systems B interfaces
lt-0/1/0]
user@R1# set
unit 2 description to-A
user@R1# set
unit 2 encapsulation ethernet
user@R1# set
unit 2 peer-unit 1
user@R1# set
unit 2 family inet address 10.10.10.2/30
user@R1# set
unit 5 description to-C
user@R1# set
unit 5 encapsulation ethernet
user@R1# set
unit 5 peer-unit 6
user@R1# set
family inet address 10.10.10.5/30
user@R1# up
[edit logical-systems B interfaces]
user@R1# set
lo0 unit 2 family inet address 192.163.6.4/32
user@R1# exit
[edit]
user@R1# edit
logical-systems C interfaces lt-0/1/0 unit 6
[edit logical-systems C interfaces
lt-0/1/0 unit 6]
set description to-B
set encapsulation ethernet
set peer-unit 5
set family inet address
10.10.10.6/30
user@R1# up
user@R1# up
[edit logical-systems C interfaces]
set lo0 unit 3 family inet
address 192.168.40.4/32
- Configure
BGP.
On Logical System A, the neighbor statements are
included for both Device B and Device C, even though Logical System A is not
directly connected to Device C.
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[edit logical-systems A protocols
bgp group internal-peers]
user@R1# set
type internal
user@R1# set
local-address 192.168.6.5
user@R1# set
export send-direct
user@R1# set
neighbor 192.163.6.4
user@R1# set
neighbor 192.168.40.4
[edit logical-systems B protocols
bgp group internal-peers]
user@R1# set
type internal
user@R1# set
local-address 192.163.6.4
user@R1# set
export send-direct
user@R1# set
neighbor 192.168.40.4
user@R1# set
neighbor 192.168.6.5
[edit logical-systems C protocols
bgp group internal-peers]
user@R1# set
type internal
user@R1# set
local-address 192.168.40.4
user@R1# set
export send-direct
user@R1# set
neighbor 192.163.6.4
user@R1# set
neighbor 192.168.6.5
- Configure
OSPF.
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[edit logical-systems A protocols
ospf area 0.0.0.0]
user@R1# set
interface lo0.1 passive
user@R1# set
interface lt-0/1/0.1
[edit logical-systems A protocols
ospf area 0.0.0.0]
user@R1# set
interface lo0.2 passive
user@R1# set
interface lt-0/1/0.2
user@R1# set
interface lt-0/1/0.5
[edit logical-systems A protocols
ospf area 0.0.0.0]
user@R1# set
interface lo0.3 passive
user@R1# set
interface lt-0/1/0.6
- Configure
a policy that accepts direct routes.
Other useful options for this scenario might be to accept routes
learned through OSPF or local routes.
content_copyzoom_out_map
[edit logical-systems A
policy-options policy-statement send-direct term 2]
user@R1# set
from protocol direct
user@R1# set
then accept
[edit logical-systems B policy-options
policy-statement send-direct term 2]
user@R1# set
from protocol direct
user@R1# set
then accept
[edit logical-systems C
policy-options policy-statement send-direct term 2]
user@R1# set
from protocol direct
user@R1# set
then accept
- Configure
the router ID and the autonomous system (AS) number.
content_copyzoom_out_map
[edit logical-systems A
routing-options]
user@R1# set
router-id 192.168.6.5
user@R1# set
autonomous-system 17
[edit logical-systems B
routing-options]
user@R1# set
router-id 192.163.6.4
user@R1# set
autonomous-system 17
[edit logical-systems C
routing-options]
user@R1# set
router-id 192.168.40.4
user@R1# set
autonomous-system 17
Results
From configuration mode,
confirm your configuration by entering the show logical-systems command. If the
output does not display the intended configuration, repeat the configuration
instructions in this example to correct it.
user@R1> show bgp neighbor logical-system A
user@A> show bgp group logical-system A
user@A> show bgp summary logical-system A
user@A> show route protocol bgp logical-system A
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