Does looping happen on (RIP,OSPF,EIGRP) ?

[pvanvu]

HI guys
Based on the picture below with 3 Routes are connected together as a triangel , I have some questions still confusing :

- In Static Route , we have Floating Static Route act as a Backup route . If one link failed , the Backup link will be activated . But both links can not be activated at the same time because it will cause "looping" in the Network

- In RIP , OSPF , EIGRP , I never seen any lines mention about the Backup route , because both links are enabled at the same time without any additional configurations like " Floating Static Route ".

My question :
Does looping happen on (RIP,OSPF,EIGRP) ?

 

[MtnMan]

Only the route with the lowest AD will be put in the routing table, and that is why every routing protocol, plus directly connected and static have a different AD value.

 

[Gryz]

HI guys
Based on the picture below with 3 Routes are connected together as a triangel , I have some questions still confusing :

As I've written before, you should get yourself a good book. Not just study random cisco cases. I don't think you have a good understanding of the basic concepts. If you do get that, all your current questions will be much easier to answer/understand.

- In Static Route , we have Floating Static Route act as a Backup route . If one link failed , the Backup link will be activated .

True.

But both links can not be activated at the same time because it will cause "looping" in the Network

The reason they are not activated at the same time is, as MntMan says, because of Administrative Distance (AD). Floating static routes have a worse AD. And thus will not be installed in the routing-table if there is already another (static) route with a better AD.

This has nothing to do with preventing loops.
Of course, if you configure wierd/wrong floating static routes, you can create loops. But the concept of floating static routes has nothing to do with loops. Or preventing loops.

If you want two static routes pointing to the same destination, over 2 different path, that is all possible and legal. It just means that traffic towards that destination will be "load balanced" over those 2 paths.

In RIP , OSPF , EIGRP , I never seen any lines mention about the Backup route , because both links are enabled at the same time without any additional configurations like " Floating Static Route ".

IGPs don't have "backup routes". They just keep re-computing the routing-table any time they think that is necessary. So one second you might have this route in your routing table "route to 20.20.0.0/16 via interface Serial0", and a few seconds later it might change into "route to 20.20.0.0/16 via interface Serial 1". Even when Serial0 is still up. It depends on the overall topology of the network.

Static routes only know about the state of the router that the static route is configured on. Therefor (floating) static routes can not do a lot of failure-recovery. They literally don't know if something failed that is not inside the router or attached to the router.

My question :
Does looping happen on (RIP,OSPF,EIGRP) ?

I can talk for hours about this subject. Days probably. But I will only confuse you. So let's keep it simple.

Routing protocols (also called IGPs, Interior Gateway Protocols) are designed and built and optimized to compute loop-free routes inside a network. So your answer is: yes.

However, right when something changes in the network (aka a failure somewhere), there is some communication between routers. And then they need to do some computation. While this is going on in the network, some routers might have outdated info, and some might have new info. And therefor their routing tables might not be in sync. And that can cause routing loops. But those routing loops are temporary. Also called "transient loops".

In modern networks, with modern routers, OSPF and IS-IS should be able to converge (change their state to the new topology) in under a second. A few hundreds of milliseconds. If you use RIP, it might take a few minutes at worse. I hope this answer is good enough for you. Because I'm gonna explain further.

Again, get yourself a good book (or two).
I always liked "Internetworking with TCP/IP, volume 1" by Douglas Comer. It's been a couple of decades since I read introduction books about network. Maybe other posters here have more suggestions. The cisco documenation is probably excellent. But maybe not for a beginner. (My apologies that I call you a beginner. But it seems you can use some help with some of the basic concepts).

 

[pvanvu]

Only the route with the lowest AD will be put in the routing table, and that is why every routing protocol, plus directly connected and static have a different AD value.

Thank MtnMAN :thumbsup:

As I've written before, you should get yourself a good book. Not just study random cisco cases. I don't think you have a good understanding of the basic concepts. If you do get that, all your current questions will be much easier to answer/understand.

True.

The reason they are not activated at the same time is, as MntMan says, because of Administrative Distance (AD). Floating static routes have a worse AD. And thus will not be installed in the routing-table if there is already another (static) route with a better AD.

This has nothing to do with preventing loops.
Of course, if you configure wierd/wrong floating static routes, you can create loops. But the concept of floating static routes has nothing to do with loops. Or preventing loops.

IGPs don't have "backup routes". They just keep re-computing the routing-table any time they think that is necessary. So one second you might have this route in your routing table "route to 20.20.0.0/16 via interface Serial0", and a few seconds later it might change into "route to 20.20.0.0/16 via interface Serial 1". Even when Serial0 is still up. It depends on the overall topology of the network.

Static routes only know about the state of the router that the static route is configured on. Therefor (floating) static routes can not do a lot of failure-recovery. They literally don't know if something failed that is not inside the router or attached to the router.

I can talk for hours about this subject. Days probably. But I will only confuse you. So let's keep it simple.

Routing protocols (also called IGPs, Interior Gateway Protocols) are designed and built and optimized to compute loop-free routes inside a network. So your answer is: yes.

However, right when something changes in the network (aka a failure somewhere), there is some communication between routers. And then they need to do some computation. While this is going on in the network, some routers might have outdated info, and some might have new info. And therefor their routing tables might not be in sync. And that can cause routing loops. But those routing loops are temporary. Also called "transient loops".

In modern networks, with modern routers, OSPF and IS-IS should be able to converge (change their state to the new topology) in under a second. A few hundreds of milliseconds. If you use RIP, it might take a few minutes at worse. I hope this answer is good enough for you. Because I'm gonna explain further.

Again, get yourself a good book (or two).
I always liked "Internetworking with TCP/IP, volume 1" by Douglas Comer. It's been a couple of decades since I read introduction books about network. Maybe other posters here have more suggestions. The cisco documenation is probably excellent. But maybe not for a beginner. (My apologies that I call you a beginner. But it seems you can use some help with some of the basic concepts).

Thank Gryz for very detail info
You are correct , I'm just a beginner , I'm now in CCNA2 class . Actually , I had all the books I need but I don't have enough time to read every little detail in the book because I work in the morning , and have class at night . It's hard to remember everything at once , but I'm trying to understand all the important parts ( such as the questions I asked you guys ) and bookmark them for reference

Only working on the real network , or practice on Packet Tracer made me think about these questions . otherwise , just reading book is helpless , and hard to remember without practicing on the real NW . I will gain more knowledge time by time

Again thank Gryz a lot :thumbsup::thumbsup::thumbsup::thumbsup::thumbsup:

 

[sactwnguy]

Also the chances of getting a routing loop with just EIGRP and OSPF is pretty low(does anyone still use RIP?), its redistribution between routing protocols that will get you every time.