Does subnet mask add Router utilization?

[kulagun]

We want to use a 10.x.0.0 /16 subnet instead of a 10.x.x.0 /24. Will this add a bunch of overhead to the router to process the 16 bit mask instead of the 24. If so does anyone know how much?

Thank You

 

[tcvander]

The way the router does it's lookups is based on the longest match, so if you shorten the match; i.e from 24 to 16 bits that lookup will be shorter and less processing power.
Also, as an FYI you will save memory space also, not as many subnets to store. Todd VanDerwerken, CCNA, CCDA
Technical Consultant

http://www.ciscolinks.net

 

[kulagun]

Is there any way to tell how much utilization it will take up? could it be with 60 networks, 1%,5% or 50%

Thanks

 

[tcvander]

That is a hard one to answer, because there are some many different factors, routing protocol, stability of the network, etc. What does it show now when you enter the command "show ip route sum"?
Look here for more info:

http://www.cisco.com/warp/public/63/highcpu.html#1

Todd VanDerwerken, CCNA, CCDA
Technical Consultant

http://www.ciscolinks.net

 

[kulagun]

Also is EIGRP more efficient than OSPF? We have a debate here going in our IT DEPT.

Thanks

Route Source Networks Subnets Overhead Memory
connected 0 13 1116 1872
static 2 8 1000 1440
eigrp 1 2 44 6988 6624
ospf 1 0 17 1088 2448
Intra-area: 14 Inter-area: 0 External-1: 0 External-2: 3
NSSA External-1: 0 NSSA External-2: 0
rip 0 4 256 576
internal 5 5820
Total 9 86 10448 18780

 

[wybnormal]

You will be arguing to the end of time. Which is more *efficent* depends on ALOT of other things. How is the addressing configured? lots of broken up subnets? summerization? lots of changes to the links.. ie.. flapping? and the topper which makes the WHOLE thing moot.. like apples and oranges is that EIGRP suports multiple protocols where OSPF only supports IP. If one item like EIGRP has an inherently higher overhead due to supporting more then one protocol, you can not compare it against a routing protocol that only supports one protocol.

I will say this.. the official Cisco book on designing with EIGRP is about 1" thick.. the OSPF book is around 2" thick. OSPF has alot more functionality offered and is more flexible on IP. Of course, you can also it's more complicated

MikeS
Find me at

http://www.packetattack.com

"Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots."
Sun Tzu

 

[tcvander]

I agree with wybnormal, OSPF is far more compilcated then EIGRP to setup, with having to figure out all the area structure and all. EIGRP doesn't have that.
From a CPU prespective, every time OSPF has to converge it has to re-run Dijkstra algorithm which is very CPU intensive.
Whereas EIGRP builds Feasible successors for each route and thereby doesn't require the algorithm to re-run.
Todd VanDerwerken, CCNA, CCDA
Technical Consultant

http://www.ciscolinks.net