Posts tagged OSPF

Route Summarization for the ERS8600

8 months ago
by Paul A. Leroux in , ,

As networks grow in size the routing tables on each router grows as well. As a result the overhead to process the routes can grow exponentially and take resources away from other functions the router can be performing. As well, large routing tables can be difficult to read quickly, efficiently and troubleshoot. You can make your life extremely easy if you engineer your IP addressing using an harmonious numbering system and avoid using a discontinuous network address scheme. If you adhere to these methods and use CIDR addresses you can also take advantage of Route Summarization (aka Route Aggregation)

An example of a route summariztion would be: If you have an ASBR that manages five 24bit networks.

172.16.0.1/24
172.16.1.1/24
172.16.2.1/24
172.16.3.1/24
172.16.4.1/24

In a neighbouring router’s table, these networks will be listed as attached networks with a next hop and value. And each route will be advertised to the LSDB. We can reduce the amount of advertisements by summerizing these 5 networks on the ASBR as one large Network so the neighbouring router will only receive one advertisement. This is accomplished by using a CIDR mask length that will encompass the entire range of the 5 example networks.

The five networks listed above consist of the range 172.16.0.1 – 172.16.4.255. This can be summarized as 172.16.0.0/21 or 172.16.0.0/255.255.248.0

To accomplish this you will need to understand CIDR, VLSM, IP, and binary Math.  The best site I have found that explains the math behind the calculations is.  http://subnettingmadeeasy.blogspot.com/2007/11/router-summarization.html note: the author of this article makes some great observations on how summarizing your routes can cause issues. He also describes some great work arounds.

or if you are like me. You can use an online calculator. The best one I have found is http://buchananweb.co.uk/security51.aspx

An ERS8600 CLI example of the route summary described above would look like this.

ip ospf admin-state enable
ip ospf router-id 172.16.0.0
ip ospf enable
ip ospf area 0.0.0.1 create
ip ospf area 0.0.0.1 range 172.16.0.0/255.255.248.0 create advertise-mode summarize lsa-type summary-link advertise-metric 10
OSPF RIP BGP Nortel Lab -v1

Interconnecting Avaya(Nortel) OSPF and RIP Network Devices.

8 months ago
by Paul A. Leroux in ,

It is a safe assumption that most “greenfield” networks are built using OSPF. But a time could come when you have to add a RIP network device to your OSPF network.  In the Nortel/Avaya world this case could be true if you have an existing OSPF Network consisting of ERS8600′s and you wish to add an ERS5500, ERS4500 or a legacy Cisco Device. Should this requirement arise you will need to research OSPF Redistribute functions. OSPF Redistribute configurations will accept external routes from devices running different routing protocols into the OSPF domain at the ASBR.

The Setup
In the scenario I have built for you I have three ERS8600′s participating in a simple OSPF area. Each ERS8600 has two vlans, as well as two BRouter ports configured as the OSPF Broadcast interfaces.  The BRouter ports act as the interconnections for the three routers.  The fourth router added to the network is an ERS5510. The ERS5510 only supports RIP so it will be connected to Router #3 because Router #3 will assume the role of the ASBR for the OSPF Area. The role of the ASBR is important because it will be the router that will manage of the RIP routes from the ERS5510 and will need to be configured according with the appropriate routing Redistribute policies.

The Configuration

ERS8600#3 BRouter Port Config

ethernet 1/5 ip create 192.168.13.1/255.255.255.0 13 mac_offset 4

ERS5510 BRouter Port Config

brouter port 1 vlan 13 subnet 192.168.13.2/24

ERS8600#3 OSPF Config

ip ospf admin-state enable
ip ospf as-boundary-router enable
ip ospf router-id 172.16.5.1
ip ospf enable

ERS8600#3 RIP Config

ip ospf redistribute rip create
ip ospf redistribute rip metric 10
ip ospf redistribute rip enable
ethernet 1/5 ip rip enable

ERS8600#3 Route Policy

ip route-policy "to other domain" seq 1 create
ip route-policy "to other domain" seq 1 enable
ip route-policy "to other domain" seq 1 action permit
ip route-policy "to other domain" seq 1 match-protocol local|static|ospf
ip route-policy "to other domain" seq 1 set-metric 10
ip rip interface  192.168.13.1 out-policy "to other domain"

ERS8600#3 OSPF Redistribute Function.

ip ospf redistribute rip create
ip ospf redistribute rip metric 10
ip ospf redistribute rip enable

Outcome
Now that Router#3 is configured as the ASBR and configured to accept the RIP routes from the 5510 the two vlans on the 5510 will be visible to the other devices in the OSPF area.

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