Signed-off-by: Ben Pfaff <b...@nicira.com>
---
FAQ | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)
diff --git a/FAQ b/FAQ
index 2912ae3..df7b6ef 100644
--- a/FAQ
+++ b/FAQ
@@ -935,6 +935,50 @@ A: Yes. Use an "internal port" configured as an access
port. For
ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
ifconfig vlan9 192.168.0.7
+ See also the following question.
+
+Q: I configured one IP address on VLAN 0 and another on VLAN 9, like
+ this:
+
+ ovs-vsctl add-br br0
+ ovs-vsctl add-port br0 eth0
+ ifconfig br0 192.168.0.5
+ ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
+ ifconfig vlan9 192.168.0.9
+
+ but other hosts that are only on VLAN 0 can reach the IP address
+ configured on VLAN 9. What's going on?
+
+A: RFC 1122 section 3.3.4.2 "Multihoming Requirements" describes two
+ approaches to IP address handling in Internet hosts:
+
+ - In the "Strong ES Model", where an ES is a host ("End
+ System"), an IP address is primarily associated with a
+ particular interface. The host discards packets that arrive
+ on interface A if they are destined for an IP address that is
+ configured on interface B. The host never sends packets from
+ interface A using a source address configured on interface B.
+
+ - In the "Weak ES Model", an IP address is primarily associated
+ with a host. The host accepts packets that arrive on any
+ interface if they are destined for any of the host's IP
+ addresses, even if the address is configured on some
+ interface other than the one on which it arrived. The host
+ does not restrict itself to sending packets from an IP
+ address associated with the originating interface.
+
+ Linux uses the weak ES model. That means that when packets
+ destined to the VLAN 9 IP address arrive on eth0 and are bridged to
+ br0, the kernel IP stack accepts them there for the VLAN 9 IP
+ address, even though they were not received on vlan9, the network
+ device for vlan9.
+
+ To simulate the strong ES model on Linux, one may add iptables rule
+ to filter packets based on source and destination address and
+ adjust ARP configuration with sysctls.
+
+ BSD uses the strong ES model.
+
Q: My OpenFlow controller doesn't see the VLANs that I expect.
A: The configuration for VLANs in the Open vSwitch database (e.g. via
--
1.7.10.4
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