different IP address of the same subnet onto two lan cards

[dscao]

They will not function reliably if I assign two different IP addresses of the same subnet onto two physical lans of the same HP-UX. I'd like to know why!
Thanks.

[Steven E. Protter]

Shalom,

OS design.

HP-UX only permits one network per NIC. You need a second NIC card to have a second network(subnet) on an HP-UX system.

There are some indications that this restriction may be lifted, but notthing concrete thus far.

SEP

[Emil Velez]

you can put multiple IPs for the same subnet on a single card that is a functionality of ifconfig and utilized by the ServiceGuard product. Auto Port aggregation allows multiple NIC cards to be bound together for failover and allow them to be trated as one.

ServiceGuard does provide failover if a nic card fails to move traffic automatically to another nic card or allow one nic card to be a standby for multiple physical cards so if any one fails it uses the standby one. TCP connections usually do not have a issue with this.

What are you trying to accomplish with this failover or more capacity ?

If more capacity APA.. if failover then ServiceGuard.

Good luck

Emil

[John Payne_2 · Accepted solution]

dscao,

I'm not endorsing this should be done as a general rule. (I personally don't see the need for it on the same subnet, for exactly the reasons listed above...) Should you have some sort of business need requiring it, (which I would myself call 'an irrational business need...') you may want to look at the ndd parameter 'ip_strong_es_model'. I use it for enabling traffic from 2 interfaces on different subnets, and getting it so that if the traffic comes in on one interface, it will go back out on that interface, not the 'default' route.

Again, it shouldn't be necessary to have 2 IPs on 2 different NICs under normal condictions.

Hope it helps
John

From ftp://ftp.cup.hp.com/dist/networking/briefs/annotated_ndd.txt

ip_strong_es_model:

Controls support for "Strong End-System Model" described in
RFC1122, Section 3.3.4.2. When enabled, packet source addresses
(and therefore interfaces on a multihomed host) affect selection
of a gateway for outbound packets. Set to 0 to disable; set to 1
to enable. [0,1] Default: 0 (disable)

Setting this value to one will have the beneficial effect of allowing
(should they be desired) per-interface default routes. It also means
that if a packet is received on a given interface, the reply to that
packet will be sent-out that interface. This can be useful if one is
in the rare situation of needing to have separate physical (in the
context of IP - see ip_ill_status) interfaces configured with IP
addresses in the same subnet. Generally though, using Auto Port
Aggregation (APA) to create one virtual interface with a logical
interface for each address is a more robust solution.

Also, when ip_strong_es_model is set to a value of one, IP datagrams
arriving on the "wrong" interface (one that does not have an IP
address which matches the IP datagrams' destination IP address) are
discarded. If one is using IP address aliases on the loopback (lo0)
interface in support of functionality such as hardware load balancer
triangle routing, setting ip_strong_es_model to a value of one may
result in loss of connectivity for the virtual IP address.

[dscao]

Thanks. I think I've got the necessary materials for my explanation to my customer, though I still can not figure it out why a gateway/router can not be a "Strong End System".

[Tor-Arne Nostdal]

Hi dscao
Since you're a new member in the forum pls. read:

http://forums1.itrc.hp.com/service/forums/helptips.do?#33