OSPF hello and LSA

[hadisharifi]

Hi,

My OSPF neighbors reset them selves, I want to apply qos for HELLO and SLA traffic. I want to mark them but not sure how much bandwidth I need to allocate for it.

Can someone please advise or an approperaite estimate/config?

Regards

[mheusing]

Hi,

you can create a policy marking local traffic - originated by the router - with a specific IP preference value. Note, by default OSPF packets will be marked with IP preference 6. On the interfaces you can then include a class for this traffic in your policy-map. It is hard to tell which amount of bandwidth you should allocate, as this depends on parameters like interface bandwidth and also on how much local traffic the router generates. An example:

ip local policy route-map IPP6

route-map IPP6 permit 10

match ip address LocalPrioTraffic

set ip precedence 6

ip access-list extended LocalPrioTraffic

permit ospf any any

permit tcp any any eq telnet

permit tcp any eq telnet any

permit udp any any eq snmp

!

! Match your local traffic here, like telnet, SNMP, IPSLA, etc.

!

class-map match-any NMS

match ip precedence 6

policy-map MyQoS

class NMS

bandwidth percent 10

class class-default

fair-queue

random-detect

interface Serial0

ip address 10.1.1.1 255.255.255.252

bandwidth 128

service-policy output MyQoS

For a detailed syntax description please have a look at

http://www.cisco.com/en/US/docs/ios/12_2/iproute/command/reference/1rfindp1.html#wpxref37880

Be aware the service-policy will also "catch" all transit telnet traffic, respectively all traffic marked with IP precedence 6 and you need to allocate enough resources for the combined traffic (local+transit).

Hope this helps! Please use the rating system.

Regards, Martin

[hadisharifi]

thanks for the suggestion, do I need to set IP LOCAL-POLICY given that the ospf traffic are marked with IP precedence 6. what about the policy below? isn't it enough to treat the ospf traffic as desired.

clss-map OSPF-TRAFFIC

match ip precedence 6

policy-map MY-POLICY

class OSPF-TRAFFIC

bandwidth percent 10

Given that OSPF traffics are marked with IP precedence 6 by default, I can just match them and give it 10% of the bandwidth.

Regards

[Giuseppe Larosa]

Hello,

a reference document could be RFC 1245 "OSPF Protocol Analysis" where OSPF bandwidth usage is studied.

You have to take in account that even in a stable network LSAs are refreshed evry 30 minutes.

The bandwidth usage depends from the number of IP routes in the OSPF database.

OSPF packets have usually IP Prec = 6 so you can create a class-map for them and defines some bandwidth for it in a CBWFQ scheduler.

You don't need to mark OSPF packets.

Received OSPF packets are placed in a queue for process switching.

Because the bandwidth command in CBWFQ does not imply a fixed reservation don't be afraid of giving too much bandwidth to OSPF traffic.

Some platforms like a C3640 and other small ones have a system queue for routing traffic but other platforms like c7500 and 12000 haven't got one and you need to define one.

hope to help

Giuseppe

[hadisharifi]

Thanks for the suggestion, this is what I am leaning towards as well and I have asked "mheusing" to confirm.

[bvsnarayana03]

By default only 75% of the bandwidth configured on an ineterface is used by traffic. Rest 25% is reserved for use by protocol related traffic which include the Hello's & LSA's u were talking about. So if u are using default interface configurations, there seems no need to use any qos features.

[hadisharifi]

Can you please post us the link for reference as I am not quite sure what the default interface configuration is. Because by default an interface doesn't have a bandwidth statement but it it's configured I assume it changes the default behaviour and there are other similar configs...

[Giuseppe Larosa]

Hello,

this is not true for all the router platforms.

Best Regards

Giuseppe