randylf
join:2008-05-21
Tempe, AZ
| static route question
I need some assistance in understanding the process behind static routes getting removed from the routing table.
I have read all kinds of CCNA material, and alot of google sources and cant get an answer.
Do cisco routers rely STRICTLY on a line/protocol link down state to determine if a static route is unreachable and should be removed from the routing table?
If so, then if an interface a static route is using stops passing L3 traffic, but the L2/L1 status is still up, will the route remain in the routing table?
How does one overcome this limitation besides using IP SLA? |
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TomS_
debugger it
Premium,MVM
join:2002-07-19
Australia
| said by randylf  :How does one overcome this limitation besides using IP SLA? With a routing protocol, such as OSPF, EIGRP, or BGP.
These routing protocols (and all others) maintain adjacencies or neighborships by sending out hello messages at regular intervals. If they stop receiving these messages, it can be assumed there is something wrong, and the session to which ever peer has stopped sending hellos is shutdown or deleted and any routes received from it are removed from the routing table.
This helps you deal with layer 1-3 failures. |
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aryoba
Premium,MVM
join:2002-08-22
edit:
May 21st, @10:08AM
| reply to randylf
said by randylf :Do cisco routers rely STRICTLY on a line/protocol link down state to determine if a static route is unreachable and should be removed from the routing table? By default, yes.
said by randylf :If so, then if an interface a static route is using stops passing L3 traffic, but the L2/L1 status is still up, will the route remain in the routing table? Yes
said by randylf :How does one overcome this limitation besides using IP SLA? Beside using dynamic routing protocol, you can use similar trick as IP SLA which is the good old HSRP or VRRP. Set which gateway interface to be the preferred one. Also set the HSRP mechanism to monitor the up/down interface.
However using dynamic routing protocol such as BGP between your network and your ISP to provide the reliable default gateway route to the Internet is the best solution.
said by randylf :I need some assistance in understanding the process behind static routes getting removed from the routing table. I have read all kinds of CCNA material, and alot of google sources and cant get an answer. Have you read "Cisco IP Routing: Packet Forwarding and Intra-domain Routing Protocols" by Alex Zinin? I believe this book will provide the answer you are looking for. Happy reading  |
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randylf
join:2008-05-21
Tempe, AZ | Im actually reading the BSCI CCNP book right now which I believe covers most of the same topics correct?
If not, I will get to that book after this one.
Thanks alot. |
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aryoba
Premium,MVM
join:2002-08-22
edit:
May 22nd, @11:15AM
| Those CCNP BSCI books may cover the same topics. However the BSCI books don't have the same feel or the same flow either.
The BSCI books typically are just dumping routing theories off Cisco website or off prior edition of BSCI books with probably some additions. In other words, BSCI books are just made in rush to make a quick buck without actually putting a real genuine efforts from the "real engineers" to create a decent book.
The Alex Zinin book however provides "the real meat" that every Cisco certified engineers including CCNA certified people must know cold.
For a complete understanding of routing topics, you may want to read both Alex Zinin and the CCNP books. |
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belushi
Premium,MVM
join:2000-11-08
Twinsburg, OH
| I haven't read that one, I've found the following two books to be pretty much all encompassing on routing protocols:
CCIE Professional Developement Routing TCP/IP Volumes 1 and 2. Both by Jeff Doyle and Jennifer Carroll.
The first is mostly IGPs and some fundamentals. The second focuses on BGP, Multicast, redistribution, etc. They are basically mainstays for CCIE studies and such are extremely detailed. However, I always found the basic Cisco Press books to be an easier read.
Obviously there are more complete books on each individual technology, but these are pretty good. |
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