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旧 2004-06-08, 03:19   #16
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最初由 teru 发布
Yes. But how about the feature of OSPF Incremental SPF since 12.(2)18s to lower the SPF load?
lower the SPF load, because it NEEDS it.

[img] [/img]new qq:1651898142 msn:net130_0 at yahoo.com
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旧 2004-06-08, 03:27   #17
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Actually I have not met SIA in eigrp, I just have found some cases in web site. I remember the web site mentioned that unstable link might cause SIA.
actually i did see this SIA things happen. when SIA, the flapping route will disappear from the down stream router's routing table, it is actually BETTER for down stream routers; all the down stream routers will think the flapping link/route is NOT reachable.
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旧 2004-06-08, 09:40   #18
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最初由 y7975 发布
interface Ethernet0
ip summary-address eigrp 1 192.168.0.0 255.255.255.192
To my strange, I remember in my lab, when I summary address in rip or eigrp with 192.168.0.0/26 or like this,their will be an error message. But today I tried with my new routers and layer3 switches but they can.
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旧 2004-06-08, 09:55   #19
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最初由 y7975 发布
timer spf is used to ajust/relay spf calculation, it does not resolve the sutiation when it is flapping/unstable. also it delay the convergence time. in large network, when you delay convergence time, have higher chance cause the LOOP.
the timer spf command will delay convergence time,but it can lower the spf calculation in unstable links. I think it's good to use the command just on routers that connected to unstable WAN links.
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旧 2004-06-08, 10:35   #20
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两位高人分析的真好,这比我看多少天书强多了
建议加精!

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旧 2004-06-08, 11:26   #21
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最初由 y7975 发布
actually i did see this SIA things happen. when SIA, the flapping route will disappear from the down stream router's routing table, it is actually BETTER for down stream routers; all the down stream routers will think the flapping link/route is NOT reachable.
But at that time, it means that all eigrp routers are recomputing. but in ospf, the recomputing just within the area.

In eigrp, when there is a topology change and there is no feasible successor, eigrp needs to send queries to all of the eigrp routers, and waits for reply, which is the reason of SIA. And in OSPF, topology change just need to flood the LSA in the same area. And in eigrp, topology change must flood to all routers, but in ospf, it's not the case if in totally stub area.

eigrp is less cpu intensive than ospf, simple to config, unequal load-balance which ospf does not have, and also route summarized feature.But I will choose ospf (may be just my preference), because I like to use stub area, totally stub area and NSSA to minimize the records in routing table. And it's not cisco proprietary protocol.

Maybe that's because of my concept is not clear enough and lack of experience, I want to ask y7975 a question: How will you choose routing protocol when you design a network and reason?
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旧 2004-06-08, 11:29   #22
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最初由 soho 发布
两位高人分析的真好,这比我看多少天书强多了
建议加精!
I also learnt alot. Thanks y7975, he always makes my concept more clear.


For me, it's a long way to become a real expert.
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旧 2004-06-08, 12:24   #23
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最初由 teru 发布
But at that time, it means that all eigrp routers are recomputing. but in ospf, the recomputing just within the area.
ok, if the route/link that lost is E2 in OSPF, which is using LSA type 5, it will go to all areas except stub area, does not mean "all" routers recomputing? LSA type 3, does not go to other AREAs? Then force you to configure all areas (except 0) to STUB/NSSA, just to compensate the draw back of LSA.

引用:
In eigrp, when there is a topology change and there is no feasible successor, eigrp needs to send queries to all of the eigrp routers, and waits for reply, which is the reason of SIA.
If EIGRP can get stuck in active(query without answer), for the same situation, you think OSPF will received LSA?

[quote]And in OSPF, topology change just need to flood the LSA in the same area. And in eigrp, topology change must flood to all routers, but in ospf, it's not the case if in totally stub area.[/qutoe]

EIGRP add the "stub" in 12.2 too to eliminate the query.

ok, you can configure to STUB to drop the LSA, but you heavily rely on ABR, that means on design, you are limit to connect back to AREA 0.

while i can use EIGRP easily connect any two routers. i do not have to concern about AREA.

引用:
eigrp is less cpu intensive than ospf, simple to config, unequal load-balance which ospf does not have, and also route summarized feature.But I will choose ospf (may be just my preference), because I like to use stub area, totally stub area and NSSA to minimize the records in routing table.[/qutoe]

my environment has more other protocols to deal with, espically BGP, while using EIGRP give me more room than OSPF.

give you another good reason for useing EIGRP, eigrp consider "DELAY" also, which is dynamic. espically when my high bandwidth link is congested, it will automatic bring the traffic to lower bandwidth link. OSPF can only congest ====? queuing ====> drop packets, when you have delay sensative application (voice), EIGRP give you great flexiability here.

[qutoe]question: How will you choose routing protocol when you design a network and reason?
1. $
2. vendors platform (cisco or other vendors)
3. physical connection, topology and number of nodes(layer 1 first)
4. expandabliity (connect with others)
5. other routing protocol may involve? ex. BGP
6. Firewall (such as PIX only support RIP and OSPF now)
7. VPN (such as VPN concentrator only have RIP and OSPF now)
8. delay sensative application (ex. VOICE)
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旧 2004-06-08, 12:37   #24
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感谢

高手,永远都是高手,听了TERU 和Y7976R 的对话,才发觉网络无涯。

我是一个充满朝气的年轻人。
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旧 2004-06-08, 13:13   #25
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Thank you. I am more clear now.And it's very important that if other routing protocols are involved, eigrp should be better for it's simplicity, eigrp need not think about ABR,ASBR. That's what I ignored before. Now I realized why one of our HongKong customer, use eigrp instead of ospf, and there were about a hundred of routes in the routing table.(May be because most of networks I meet are typical hub and spoke networks, which make me tend to use ospf)Also varied router roles in OSPF make the design complex, and high loading in ASR,ASBR,and core routers,also the size of ospf area needs to be concerned. But I still have 2 questions:

1.
----------------------------------------------------------------------
In eigrp, when there is a topology change and there is no feasible successor, eigrp needs to send queries to all of the eigrp routers, and waits for reply, which is the reason of SIA.
----------------------------------------------------------------------
If EIGRP can get stuck in active(query without answer), for the same situation, you think OSPF will received LSA?

If in the following topology:

LAN1--R1--R2--R3--LAN2

If LAN1 fails, link between R2 and R3 is unstable. R1 will send LSA to R2, R2 will send to R3 but may fail. I think that's no problem in OSPF but may lead SIA in EIGRP, because R1 is waiting for the reply from R3.

2. For the eigrp stub feature. In cisco document: "A stub router should not have any EIGRP neighbors other than distribution routers." So I think this means that the remote site just can have 1 router so it's an impediment to implement eigrp stub, and ospf stub area can include serveral routers.
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旧 2004-06-08, 13:35   #26
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最初由 teru 发布

If in the following topology:

LAN1--R1--R2--R3--LAN2

If LAN1 fails, link between R2 and R3 is unstable. R1 will send LSA to R2, R2 will send to R3 but may fail. I think that's no problem in OSPF but may lead SIA in EIGRP, because R1 is waiting for the reply from R3.
not a problem, SIA will just time out. (default 3 mins ?)

引用:
2. For the eigrp stub feature. In cisco document: "A stub router should not have any EIGRP neighbors other than distribution routers." So I think this means that the remote site just can have 1 router so it's an impediment to implement eigrp stub, and ospf stub area can include serveral routers.
correct. the be close to what OSPF STUB doing, EIGRP needs to do "ip summary-addr 0.0.0.0 0.0.0.0"

此帖于 2004-08-17 09:49 被 y7975 编辑。
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旧 2004-06-08, 14:33   #27
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讨论的好极了,高深问题。收藏起来好好品味品味。

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旧 2004-06-08, 15:20   #28
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此贴一定要收藏
建议版主加精,以后容易查看
顶顶!
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旧 2004-06-15, 22:29   #29
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这么好的讨论应该精华一把

顶!论坛里这样的讨论太少了!
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旧 2004-06-16, 14:04   #30
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高人啊!

英文不好的我还得吃力地看。。。。呵呵,非常感谢!

只是偶还有问题:
我的理解是ospf只有两层结构,市中心可以为area0,所有的县局及网点可以为area1或别的area。
但和省中心之间如果也要采用ospf,那么边缘路由器上是不是要起两个ospf的进程?省中心为area0,各市局为area1及其他。

这样是不是很乱?

如果市县间为eigrp的话,我就在省市间边缘路由器上加个路由汇聚就可以了吧。分发到省市间的ospf网络中是不是就可以了。

唉,谁叫俺们理论水平也不行,实际经验又少呢。
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