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LAAUDI_53196's avatar
LAAUDI_53196
Icon for Nimbostratus rankNimbostratus
Oct 31, 2011

ARP Failure on LTM

Hello,

 

 

I ain't a master but if you find this silly, please forgive me.

 

 

 

BIG IP <-> Internal VLAN <-> Cisco SW's <-> Servers

 

 

 

We have multiple Self IP's created for Internal VLAN so BIG IP can choose anyone to reach the Pool Members. We don't have SNAT enabled but NAT is enabled. ( it was already there when I checked the configuration)

 

 

 

Now, servers are using one of the self Ip as gateway IP. When ever we ping from outside network to those servers, I can see traffic hitting one of the self IP's but after that it times out. It works sometimes though..I don't understand why it is so intermittent. i did few captures but found that F5 was sending out ARP broadcasts but there wasn't any reply. Its more like (stacked switches in between) a direct connection from F5 to those servers.

 

 

 

all the Self IP addresses are part of same internal vlan and is connected to same 1.2 interface so no matter what self ip it uses, it will be going via 1.2 itself.

 

 

 

Do you think its because of arp time out? Default is 2seconds and then new request is broadcasted. Even if it, atleast for 3rd or 4th packet, it should get a reply isn't it?

 

 

 

I had a similar problem previously and I just used SNAT Automap and it worked. Stange..!!! But I can't test it out unless I am sure that it would work. (big people around and can't afford any outages etc).

 

 

 

please provide me your valuable suggestions.

 

 

 

Thank you.

 

 

 

Jack

 

config
design
  • nitass's avatar
    nitass
    Icon for Employee rankEmployee
    Oct 31, 2011
    BIG IP <-> Internal VLAN <-> Cisco SW's <-> Serversoutside network is on another side of bigip, isn't it?

     

     

    When ever we ping from outside network to those servers, I can see traffic hitting one of the self IP's but after that it times out.when pinging server, does it hit NAT or another object e.g. SNAT, virtual server?

     

     

    sol9038: The order of precedence for local traffic object listeners

     

    http://support.f5.com/kb/en-us/solutions/public/9000/000/sol9038.html

     

     

    i did few captures but found that F5 was sending out ARP broadcasts but there wasn't any reply.have you seen arp entry when running b arp on bigip?
  • LAAUDI_53196's avatar
    LAAUDI_53196
    Icon for Nimbostratus rankNimbostratus
    Nov 01, 2011
    Correct, Nitass,

     

    outside network <-> LB <-> Inside Network ( Cisco L2 sw stack ) - cisco blade sw's <-> Blade Servers

     

     

    We have NAT (destination) enabled but SNAT is disabled on F5.

     

    Sometimes, I find the arp entry in INCOMPLETE state and sometimes I find the ARP entry. It's so intermittent. Server guy replaced the NIC as well but still the same. Do you think SNAT Automap would do any help? Also, please note that we have BladeServer NIC's teamed using Smart Load Balancing so we learn two mac-addresses for one single IP.
  • nitass's avatar
    nitass
    Icon for Employee rankEmployee
    Nov 02, 2011
    i don't think snat does help. would it be possible to try to disable one nic card?

     

     

    and is this relevant?

     

     

    sol3009: Configuring BIG-IP to load balance traffic to nodes that use redundant network interface cards

     

    http://support.f5.com/kb/en-us/solutions/public/3000/000/sol3009.html