Server Load Balancing (SLB)
When you´re working on your BCMSN exam on your way to CCNP certification, you´ll read at length about how Cisco routers and multilayer switches can work to provide router redundancy - but there´s another helpful service, Server Load Balancing, that does the same for servers.
Sun Sees Red, Sues Azul
Sun Microsystem's acquisition of Cobalt Networks in September 2000 has made it back into the headlines, as Sun files a lawsuit against former Cobalt and current Azul CEO Stephen DeWitt over theft of trade secrets and violation of a non-compete agreement.
Who Will Win The Switch Wars?
Why is it that people can look at a simple sentence - and interpret it in so many ways?
Can't Connect to Internet
We talked about DNS problems at Fallure to resolve, but there are other reasons why a particular machine may be unable to browse the Internet while others on the same lan still can.
Cisco Rounding Up Digital Talent
A $250,000 promotion conducted by networking giant Cisco and Viacom's mtvU college network will support a "Digital Incubator" for broadband content.
Who Said That?
My wife and I had run out for errands and had stopped at a D'Angelo sub shop. We were just about to get out of the car when the phone rang. My wife rolled her eyes but I took the call because, well, because that's what I do. Somebody has a problem, I try to answer the phone.
BGP Adjacency States
To pass the BSCI exam, earn your CCNP certification, and become an outstanding networker, you´ve got to master the many details of BGP - and trust me, there are a lot of details to master!
Dynamic Trunking Protocol (DTP)
When you´re studying to pass the BCMSN exam on the way to earning your CCNP certification, you´re going to add to your CCNA knowledgebase every step of the way.
BCMSN exam success and earning your CCNP certification requires you to add to your knowledge of VLAN
Keep in touch (tcp keepalives etc.)
You can't please everyone, so you got to please yourself...I don't imagine Ricky Nelson was thinking about tcp timeouts and keepalives in the 70's...
Senator Proposes Net Neutrality Bill
Ron Wyden (D-Or) has introduced legislation to prevent telecoms and cable companies from developing a two-tiered network where fees would be charged to content providers to prioritize their Internet traffic...
Open Source Vyatta Takes On Hardware
After years of open source projects like Linux and MySQL
taking share from proprietary software companies, hardware
makers like Cisco and Juniper get to experience the heart-stopping
terror of open source hardware hitting the market...
Route Summarization And The OSPF Null Interface
By Chris Bryant
CCNP exam success, particularly on the BSCI exam, demands you understand the details of route summarization.
This skill not only requires that you have a comfort level with binary conversions, but you have to know how and where to apply route summarization with each individual protocol.
You also have to know the "side effects" of route summarization. With OSPF, there will actually be an extra interface created at the point of summarization, and this catches a lot of CCNP candidates by surprise. Let's take a look at the null0 interface and how it relates to OSPF summarization.
On R1, the following networks are redistributed into OSPF, and then summarized.
ip address 22.214.171.124 255.0.0.0
ip address 126.96.36.199 255.0.0.0
ip address 188.8.131.52 255.0.0.0
ip address 184.108.40.206 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute connected subnets
R1(config-router)#summary-address 220.127.116.11 252.0.0.0
The summary address appears on R2, a downstream router.
R2#show ip route ospf
O E2 18.104.22.168/6 [110/20] via 22.214.171.124, 00:00:05, Serial0
Let's go back to R1 and look at its OSPF table.
R1#show ip route ospf
O 126.96.36.199/6 is a summary, 00:01:51, Null0
Where did the null0 interface come from, and why is it there? Packets sent to the null interface are dropped, and in this case, that's a good thing.
When you configure summary routes in OSPF, a route to null0 will be installed into the OSPF routing table. This helps to prevent routing loops. Any packets destined for the routes that have been summarized will have a longer match in the routing table, as shown below...
C 188.8.131.52/8 is directly connected, Loopback17
C 184.108.40.206/8 is directly connected, Loopback16
C 220.127.116.11/8 is directly connected, Loopback19
C 18.104.22.168/8 is directly connected, Loopback18
O 22.214.171.124/6 is a summary, 00:01:51, Null0
.. and packets that do not match one of the summarized routes but do match the summary route will be dropped.
Preventing routing loops when performing route redistribution and summarization is vital. OSPF gives us a little help in that regard in this situation, and as you study more complex redistribution scenarios on your way to the CCNP and CCIE, you'll realize that we'll take all the help we can get!
About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of FREE CCNA and CCNP tutorials and daily exam questions, as well as The Ultimate CCNA and CCNP Study Packages.