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Community Member

Server with dual switch configuration ?


i have a couple servers that need redundant connection to our server farm switches (two Cat3550-12T),

on the server we have 2 NIC (1000baseT from broadcom)

we're running link aggregation 802.3ad but when i try to connect the second NIC to the second Cat3550 i receive HOSTFLAPPING error message.

is it in the spanning tree ?

where i can find the guides/config examples ?

i already try to find it but no luck...

please help me.. :((

Community Member

Re: Server with dual switch configuration ?


I think 3550s does not support spanning the ehther channel acrros the switches

Community Member

Re: Server with dual switch configuration ?

Hi too,

So what would you suggest then ? :)

how about if i use Smart Load Balancing on the server side (if i'm not wrong SLB still using a different MACAddress on both NIC) so this would fix the hostflapping issue, right ?

Please advice

Community Member

Re: Server with dual switch configuration ?

right, Broadcom's SLB should work for you

different MAC for each NIC

balancing based on IP

have a look at

Community Member

Re: Server with dual switch configuration ?

Hi Petr,

Thank you very much for your suggest :)

after look in the reference u gave me

i don't quite understand whatis the PASS mean.

is it the client session to the server still remains or the clients still needs to "reconnect" to the server ?

How about on mySAP environment is it the same?

And one more thing i don't quite understand about the "script" in the reference.

If the "script" was to refresh the ARP,

what if i put static ARP on my L3 switch(4503)?

so my conclusion is :

I'll try to use the Broadcom's SLB and then if still fail i'll configure the second NIC to be "Standby Adapter" on the BASP team. Is it right ?

Please advice.

Thank you very much.

Sabirin Supranto

Community Member

Re: Server with dual switch configuration ?


PASS - if you reffer to Figure 3, than I reckon it means - the failover test PASSed sucessfuly

client session - in case, that the session is TCP/IP then it should survive, of course 'it depends'

mySAP - sorry no experience with this

application happy with sporadic 10 second packet delay will have no problem

in case of hard requirement of 1 second response, you will probably have to look elsewhere

like Industrial/Telco switches with millisecond failover times

ARP - everybody on the way Server <-> Client keeps ARP table (IP/MAC)

when the situation changes (failover), it may take some time for all of them to update the ARP tables

the script was used to decrease this time

where comes from this 4503, so far we had only two 3550?

static ARP entry - in your case you would like to have ARP as dynamic as possible

standby adapter - ok, now the truth, I'm using Intel not Broadcom

Intel has mode Adapter Fault Tolerance (AFT) which works fine (1-3 seconds for failover)

there are things possible to tune, but at least network topology and operating system used will be needed


Community Member

Re: Server with dual switch configuration ?

For IEEE to work accross switches you will need switches supporting dynamic

Dynamic is the magic word, look in switch documentation if you are lucky.

Regarding your hostflapping - the team is using the same MAC address for all adapters so your switch sees the same MAC on different ports. Once on port, where your server is connected and second time on port connected to the other switch.


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