Design Principles

1. The ring topology is preferred for IPRAN implementation
2. There is one aggregation IS-IS process for the aggregation layer and multiple IS-IS processes for the access layer.
3. Each ring is assigned a different IS-IS process to separate it from other rings.
4. A cost of 100 is configured for connection between CSGs and ASGs to CSGs, a cost of 50 is configured between ASGs and RSGs and a cost of 10 is configured between RSGs.
5. It is recommended to close the access IS-IS process between the ASGs.
6. Always use route policies when importing routes between access and aggregation processes.

Topology Diagram

We have a network with one aggregation ring connecting RSGs to ASGs and two access rings connecting the CSGs to ASGs. We configure IS-IS process 100 for the aggregation ring 1, IS-IS process 20 for access ring 1 and IS-IS process 30 for access ring 2.

Configuration Step 1: Configure system name, interfaces and IS-IS on all routers. Enable IS-IS on the interfaces.

*******************************RSG01
sys
sysname RSG01
#
isis 100
is-level level-2
is-name RSG01
cost-style wide
network-entity 49.0100.0010.0100.1001.00
#
interface Loopback0
ip address 1.1.1.1 32
isis enable 100
#
interface GigabitEthernet0/0/0
description TO ASG04 GE 0/0/2
ip address 10.10.10.2 31
isis enable 100
isis cost 50
#
interface GigabitEthernet0/0/1
description TO ASG02 GE 0/0/0
ip address 10.10.10.10 31
isis enable 100
isis cost 50
#
interface GigabitEthernet0/0/2
description TO RSG02 GE 0/0/2
ip address 10.10.10.0 31
isis enable 100
isis cost 50
#
commit

********************************RSG02
sys
sysname RSG02
#
isis 100
is-level level-2
is-name RSG01
cost-style wide
network-entity 49.0100.0020.0200.2002.00
#
#
interface Loopback0
ip address 2.2.2.2 32
isis enable 100
#
interface GigabitEthernet0/0/0
description TO ASG03 GE 0/0/2
ip address 10.10.10.4 31
isis enable 100
isis cost 50
#
interface GigabitEthernet0/0/1
description TO ASG01 GE 0/0/0
ip address 10.10.10.6 31
isis enable 100
isis cost 50
#
interface GigabitEthernet0/0/2
description TO RSG01 GE 0/0/2
ip address 10.10.10.1 31
isis enable 100
isis cost 50
#
commit

************************************ASG01
sys
sysname ASG01
#
isis 100
is-level level-2
is-name ASG01
cost-style wide
network-entity 49.0100.0040.0400.4004.00
#
isis 20
is-level level-2
is-name ASG01
cost-style wide
network-entity 49.0020.0040.0400.4004.00
#

interface Loopback0
ip address 4.4.4.4 32
isis enable 100
#
interface GigabitEthernet0/0/0
description TO RSG01 GE 0/0/1
ip address 10.10.10.11 31
isis enable 100
isis cost 50
#
interface GigabitEthernet0/0/1
description TO ASG02 GE 0/0/1
ip address 10.10.10.8 31
isis enable 100
isis cost 50
#
interface GigabitEthernet0/0/2
description TO CSG01 GE 0/0/1
ip address 30.30.30.0 31
isis enable 20
isis cost 100
#
commit

*******************************ASG02
sys
sysname ASG02
#
isis 100
is-level level-2
is-name ASG02
cost-style wide
network-entity 49.0100.0030.0300.3003.00
#
isis 20
is-level level-2
is-name ASG02
cost-style wide
network-entity 49.0020.0030.0300.3003.00
#
interface Loopback 0
ip address 3.3.3.3 32
isis enable 100
#
interface GigabitEthernet0/0/0
description TO RSG02 GE 0/0/1
ip address 10.10.10.7 31
isis enable 100
isis cost 50
#
interface GigabitEthernet0/0/1
description TO ASG01 GE 0/0/1
ip address 10.10.10.9 31
isis enable 100
isis cost 50
#
interface GigabitEthernet0/0/2
description TO CSG03 GE 0/0/0
ip address 30.30.30.8 31
isis enable 20
isis cost 50
#
commit

**************************************ASG03
sys
sysname ASG03
#
isis 100
is-level level-2
is-name ASG03
cost-style wide
network-entity 49.0100.0060.0600.6006.00
#
isis 30
is-level level-2
is-name ASG03
cost-style wide
network-entity 49.0030.0060.0600.6006.00
#
interface Loopback 0
ip address 6.6.6.6 32
isis enable 100
#
interface GigabitEthernet0/0/0
description TO CSG06 GE 0/0/0
ip address 20.20.20.0 31
isis enable 30
isis cost 100
#
interface GigabitEthernet0/0/1
description TO ASG04 GE 0/0/1
ip address 20.20.20.4 31
isis enable 100
isis cost 50
#
interface GigabitEthernet0/0/2
description TO RSG02 GE 0/0/2
ip address 10.10.10.5 31
isis enable 100
isis cost 50
#
commit

*******************************ASG04
sys
sysname ASG04
#
isis 100
is-level level-2
is-name ASG04
cost-style wide
network-entity 49.0100.0050.0500.5005.00
#
isis 30
is-level level-2
is-name ASG04
cost-style wide
network-entity 49.0030.0050.0500.5005.00
#
interface Loopback 0
ip address 5.5.5.5 32
isis enable 100
#
interface GigabitEthernet0/0/0
description TO CSG04 GE 0/0/1
ip address 20.20.20.6 31
isis enable 30
isis cost 100
#
interface GigabitEthernet0/0/1
description TO ASG03 GE 0/0/1
ip address 20.20.20.5 31
isis enable 100
isis cost 50
#
interface GigabitEthernet0/0/2
description TO RSG01 GE 0/0/0
ip address 10.10.10.3 31
isis enable 100
isis cost 50
#
commit

******************************CSG01
sys
sysname CSG01
#
isis 20
is-level level-2
is-name CSG01
cost-style wide
network-entity 49.0020.0070.0700.7007.00
#
interface Loopback 0
ip address 7.7.7.7 32
isis enable 20
#
interface GigabitEthernet0/0/0
description TO CSG02 GE 0/0/1
ip address 30.30.30.2 31
isis enable 20
isis cost 100
#
interface GigabitEthernet0/0/1
description TO ASG01 GE 0/0/2
ip address 30.30.30.1 31
isis enable 20
isis cost 50
#
commit

*********************************CSG02
sys
sysname CSG02
#
isis 20
is-level level-2
is-name CSG02
cost-style wide
network-entity 49.0020.0080.0800.8008.00
#
interface Loopback 0
ip address 8.8.8.8 32
isis enable 20
#
interface GigabitEthernet0/0/0
description TO CSG03 GE 0/0/1
ip address 30.30.30.4 31
isis enable 20
isis cost 100
#
interface GigabitEthernet0/0/1
description TO CSG01 GE 0/0/0
ip address 30.30.30.3 31
isis enable 20
isis cost 50
#
commit

***********************************CSG03
sys
sysname CSG03
#
isis 20
is-level level-2
is-name CSG03
cost-style wide
network-entity 49.0020.0090.0900.9009.00
#
interface Loopback 0
ip address 9.9.9.9 32
isis enable 20
#
interface GigabitEthernet0/0/0
description TO ASG02 GE 0/0/2
ip address 30.30.30.9 31
isis enable 20
isis cost 100
#
interface GigabitEthernet0/0/1
description TO CSG02 GE 0/0/0
ip address 30.30.30.5 31
isis enable 20
isis cost 50
#
commit

********************************CSG04
sys
sysname CSG04
#
isis 30
is-level level-2
is-name CSG04
cost-style wide
network-entity 49.0030.0130.1301.3013.00
#
interface Loopback 0
ip address 13.13.13.13 32
isis enable 30
#
interface GigabitEthernet0/0/0
description TO CSG05 GE 0/0/1
ip address 20.20.20.8 31
isis enable 30
isis cost 100
#
interface GigabitEthernet0/0/1
description TO ASG04 GE 0/0/0
ip address 20.20.20.7 31
isis enable 30
isis cost 50
#
commit

**********************************CSG05
sys
sysname CSG05
#
isis 30
is-level level-2
is-name CSG05
cost-style wide
network-entity 49.0030.0120.1201.2012.00
#
interface Loopback 0
ip address 12.12.12.12 32
isis enable 30
#
interface GigabitEthernet0/0/0
description TO CSG06 GE 0/0/1
ip address 20.20.20.2 31
isis enable 30
isis cost 100
#
interface GigabitEthernet0/0/1
description TO CSG04 GE 0/0/0
ip address 20.20.20.9 31
isis enable 30
isis cost 50
#
commit

********************************CSG06
sys
sysname CSG06
#
isis 30
is-level level-2
is-name CSG06
cost-style wide
network-entity 49.0030.0110.1101.1011.00
#
interface Loopback 0
ip address 11.11.11.11 32
isis enable 30
#
interface GigabitEthernet0/0/0
description TO ASG03 GE 0/0/0
ip address 20.20.20.1 31
isis enable 30
isis cost 100
#
interface GigabitEthernet0/0/1
description TO CSG05 GE 0/0/0
ip address 20.20.20.3 31
isis enable 30
isis cost 50
#
commit

Configuration Step 2: Verify IS-IS running status on the routers and check the routing tables.

When you check the routing table of CSG02, we only have routes to prefixes in access ring 1, we don’t have any routes to the aggregation ring which is running a different IS-IS process as shown below.

Similarly, the aggregation nodes have not learned any routes from the Access rings, hence the access and aggregation are isolated from each other.

To achieve connectivity between the two layers, we need to import the access IS-IS process to aggregation IS-IS process and vice versa on the ASGs. However, the access layer only need to learn about the Loopback 0 IPs of the aggregation nodes, hence we need to use a routing policy to only import Loopbacks to ASGs to access IS-IS process. Importing everything could cause loops in the network.

Configuration to import access process to aggregation process

********************************ASG01 and ASG02
ip ip-prefix ALLOW_ACCESS_LOOPBACKs index 10 permit 0.0.0.0 30 greater-equal 30 less-equal 32
route-policy ALLOW_ACCESS_LOOPBACKs permit node 10
 if-match ip-prefix acc

#
isis 100
import-route isis 20 route-policy ALLOW_ACCESS_LOOPBACKs

********************************ASG03 and ASG04
ip ip-prefix ALLOW_ACCESS_LOOPBACKs index 10 permit 0.0.0.0 30 greater-equal 30 less-equal 32
route-policy ALLOW_ACCESS_LOOPBACKs permit node 10
 if-match ip-prefix acc
#
isis 100
import-route isis 30 route-policy ALLOW_ACCESS_LOOPBACKs
commit

Configuration to import aggregation process to access process.

****************************ASG01
ip ip-prefix IMPORT_LOOPBACK0 index 10 permit 4.4.4.4 32
#
route-policy IMPORT_LOOPBACK0 permit node 10
 if-match ip-prefix IMPORT_LOOPBACK0 
#
isis 20
import-route direct cost 1000 route-policy IMPORT_LOOPBACK0 
#

****************************ASG02
ip ip-prefix IMPORT_LOOPBACK0 index 10 permit 3.3.3.3 32
#
route-policy IMPORT_LOOPBACK0 permit node 10
 if-match ip-prefix IMPORT_LOOPBACK0 
#
isis 20
import-route direct cost 1000 route-policy IMPORT_LOOPBACK0 
#

****************************ASG03
ip ip-prefix IMPORT_LOOPBACK0 index 10 permit 6.6.6.6 32
#
route-policy IMPORT_LOOPBACK0 permit node 10
 if-match ip-prefix IMPORT_LOOPBACK0 
#
isis 30
import-route direct cost 1000 route-policy IMPORT_LOOPBACK0 
#

****************************ASG04
ip ip-prefix IMPORT_LOOPBACK0 index 10 permit 5.5.5.5 32
#
route-policy IMPORT_LOOPBACK0 permit node 10
 if-match ip-prefix IMPORT_LOOPBACK0 
#
isis 30
import-route direct cost 1000 route-policy IMPORT_LOOPBACK0 
#

Verify Loopback0 IPs of ASGs are now reachable from CSGs.

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