HP-UX TCP/IP Performance White Paper, March 2008

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If the system is forwarding IP datagrams, and it is asked to forward a datagram when it knows there is a
"better" route, it will send an ICMP "Redirect" message to the source of the datagram to tell it the better
route. The system will still forward the datagram.
If the value of ip_send_redirects is set to zero, the system will still forward the wayward datagram,
but it will not tell the source that there is a better way for it to send its datagrams.
ip_send_source_quench:
Set to 1 to allow IP send ICMP "Source Quench" packets when
it encounters upstream flow control; set to 0 to disable.
[0,1] Default:1 (enable)
ip_strong_es_model:
Controls the requirement issues related to multihoming as
described in RFC1122, Section 3.3.4.2:
(A) A host MAY silently discard an incoming datagram whose
destination address does not correspond to the physical
interface through which it is received.
(B) A host MAY restrict itself to sending (non-source-
routed) IP datagrams only through the physical
interface that corresponds to the IP source address of
the datagrams.
When set to 0, it corresponds to the "Weak ES Model" and would
therefore substitute MUST NOT for MAY in issues (A) and (B).
When set to 1, it corresponds to the "Strong ES Model" and would
therefore substitute MUST for MAY in issues (A) and (B).
When set to 2, it would substitute MUST NOT for MAY in issue (A) and
SHOULD for MAY in issue (B). [0,2] Default: 0
Setting this value to one (1) 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 (1), 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.
Setting this value to two (2) will also give the effect of allowing per-interface default routes. Another feature
is that the system will try to send out the “best” matching interface, like when setting to one (1), but allow
the packet to come in on any interface, like when setting to zero (0). This could result in better link
utilization which could result in better system performance.