IS-IS and IPv6 in equal cost path topology
Network of 7609s running 12.2(18)SXE3. Two
equal cost path links between each 7609. IS-IS Level 2 routers only. When pinging an off campus IPv6 host every other packet is lost. It seems like the equal cost paths prevent an alternative path off campus but that path isn't working.
We cannot figure out where to look next.
Any thoughts ? Is this possibly an IS-IS
issue ?
Thanks
OK. I'll try. We have 5-7609s running 12.2(18)SXE3.
Each 7609 has a variety of 100/1000Base Ethernet
interfaces. They each also have one WS-X6704-10GE out
of which connections to our primary and secondary
backbones originate. This is how the routers are
interconnected.
Three of the five core routers are currently running
IS-IS. If we ssh into any router and ping
www.netbsd.org every other packet is lost.
At the end of the network are two 6506 switches each
with a 10GE module and a 1GE module.
Attached to the 1GE module are fiber links two
two different Juniper M10s which also run IS-IS
and through which we get upstream connectivity
to our provider.
All of our routers are level 2 routers in the same area.
Does this help? If not please let me know what else
you would need.
Thanks,Steve
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Hello,
This might be a simple question; using EIGRP and having 2 equal cost paths to the destination; how does the router/L3 switch route select the path from those two equal cost paths? Is there a way to force one path over anthoer?
Thanks in advance.
Best, ~sKTo answer your question we need to be clear that there are 2 parts to the decision about which path will be used to forward traffic. The first part is the identification of paths and their insertion into the routing table. This is the part where EIGRP plays a role. If EIGRP determines that there are two equal cost viable paths then both of the paths will be put into the routing table. This ends EIGRP involvement in the process. The part of the process that takes a particular packet and determines which path to use is handled by CEF. By default CEF looks at the number of available paths toward a destination and when there are multiple paths CEF will use a process that calculates based on source and destination address to choose a particular path. For the same source address and same destination address CEF should choose the same path every time.
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Hello,
I currently have two physical links connecting one data center to another. These are both 10Gb links and I have manually set the cost to the primary link to '1' and the secondary link to '10'. My question is, if I set the secondary link to '1' they would have equal cost routes. What is the selection process at this point? Will equal cost load balancing automatically kick in and use both links?
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Hi all,
I have
The network 192.168.0.0 is directly connected to Router A and B. Router A and B are redistributing the network in the ospf area 0.
Router A,B,C,D belong to the same OSPF Area.
Router C is DR. The cost of the link is indicated in the draw.
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Thanks.Hi,
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Playing with the cost to reach the ASBR and the metric of the external route I was able to figure out why the router A is the50
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If a site has two outbound WAN routers (for redundancy) that are configured as PE routers with the WAN interfaces configured with MPLS, will two LSPs be created using LDP (one from each PE) allowing the WAN routers to loadbalance traffic across the MPLS backbone?
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This is a nerdy enough qeury in reality.
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Have a look at the enclosed jpeg to get an idea.
Very simple.
Query revolves around the path selection available to OSPF.
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Appreciate any comments for debate.Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
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My guess (as I haven't re-read the RFC), selection of an ECMP to retain in a routing table (assuming all possible ECMP are not retained) and/or exactly how packets or flows are ECMP routed is implementation dependent.
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Hi,
What is the concept behind ECMP (equal cost multi path) ? Is it different for EIGRP , OSPF , ISIS etc ?
thanksDisclaimer
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Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
The concept behind ECMP is to actively and concurrently take advantage of multiple link/path bandwidth.
Oh, and to just add to what Jon has already noted, ECMP usually doesn't track actual load. So, "seeing" unequal path/link loading, especially short term, isn't unusual.
PS:
There's also unequal cost multi-path routing too - EIGRP supports that. -
RIP/EIGRP maximum number of Equal cost routes
I am looking for documentation on:
If a router has 20 equal cost routing paths and only 4 show up in the routing table, what is the determining factor that chooses which four and where are the other 16 put in case the 4 routes become unusable.
Most documentation will tell you the maximum amount and how to change it but I have not found any documentation on how EIGRP or RIP chooses the routes.You can have up to 4 by default, but you can configure the routing table to accept up to 6 on older code, and up to 8 on newer code, using the command "maximum-paths" under router eigrp. EIGRP will attempt to install all of the available paths, but the routing table will only allow it to install the first x that it installs.
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If equal cost routes exist, OSPF uses CEF load balancing?
Hi All,
Can anyone explain about:
. If equal cost routes exist, OSPF uses CEF load balancing?Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
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Rick is correct, but if his response, with mine, causes any confusion. . .
To OP's original question:
If equal cost routes exist, OSPF uses CEF load balancing?
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Does CEF load balance across multiple equal cost routes generated by OSPF?
The answer would be yes.
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OSPF Equal Cost (multiple links) but unbalanced traffic
Hi!
I would like to ask about OSPF.
We are using 4 links running OSPF point to point with equal cost to load balance MPLS L2 traffic between our two routers.
And from what we are experiencing right now is that it didnt balance the load the way it should have.
The first link always catches up the bulk of the traffic, while the remaining 3 links load balances, I would like to inquire on steps to mitigate the issue.
Appreciate if I could receive some help to solve the issue
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Best Regards,
asakurahaoI do have almost the same problem.
i have 2 x 20 Mbps Point to Point ethernet links configured with equal ospf cost and both links terminated on the single router at both ends.
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I see majority of the traffic using the link F0/0/0 and only 30% traffic using the second link F0/0/1.
I used per-packet load-sharing on these interfaces which caused throughput problems, so i removed that from the interface. Should i add some CEF commands or should try per-destination load sharing to see equal traffic on both links ? -
Hi,
We've recently inherited a job that another company was doing, so we've had our hand slightly forced on the kit and overall topology involved, however that's all fine and we can make it work.
This is a collapsed core topology with core and access switches, split over 3 blocks (fibre connections between), one core switch/stack is in block B and the other in block C, with access switches throughout.
They require all access switches to be connected to the Core in B and the Core in C, and then obviously cross connects between the two cores.
They state:
"Core switches shall be linked with 2x 1Gbps links bonded into a standard compliant Etherchannel"
"Uplinks between access and core switches shall be non-blocking - for example equal cost load balancing at layer 3, or layer 2 bonded multi-chassis Etherchannel"
The specced kit for the core are 3850's, in an ideal world I'd use VSS (Virtual Switch System) to achieve the above statements beyond repute; but this is only supported on 4500/6500 and Nexus platforms.
Do we think a cross stack etherchannel (LACP between both core switch stacks) would satisfy the above statements? Or the statements may just be badly worded...
I look forward to your thoughts and views on this! Thanks!Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
As the others have noted, the 3850s, to stack, are restricted to the length of the longest stack cables.
As you have noted, VSS physical units would allow the "logical" unit to be far apart.
For a "small" VSS core, the 4500-X might be an idea unit. (Other than cost, the 4500 would be a better choice for a core device.)
Something to watch for, or understand, when running VSS, Etherchannel doesn't load balance as it does on a single chassis or stack. VSS will avoid using the VSL cross link unless it must.
As many access switches, today, support basic L3 routing, you might also determine whether a L3 edge would be a suitable alternative choice. It would allow retention of the 3850s and can offer some advantages even over VSS. (Where VSS is very nice [as too the Nexus] supporting servers with Etherchannels.) -
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