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Re: [libvirt] [libvirt PATCHv3 00/10] DHCP snooping support for libvirt



On 10/12/2011 05:25 PM, David Stevens wrote:
Stefan Berger<stefanb linux vnet ibm com>  wrote on 10/12/2011 02:02:59
PM:

    The problem we're having at the moment is that it's not possible to
evaluate fields of packets that may have more than one possible value.
This is the general problem, the specific one being allowing multiple
MAC or IP addresses.
Stefan,
         Yes, this is why for this patchset I've added "RETURN" and made
the address checks  be "if match return" and a default drop at the
end. This code already supports multiple IP addresses for DHCP snooping,
static IP addresses (new to this version) and a combination of the
two (if both "IP" is set and "ip_learning=dhcp". Sample output using
multiple static addresses below.
         The same model can be applied to user-generated filters with:

<do a series of checks using RETURN for acceptable packets>
-j DROP

If the user filter does "RETURN", it'll apply other tests as
well. If it does "ACCEPT"/"DROP", it'll accept or drop despite
any other conditions. I'm not sure I see any need for other
tables here, though-- can you elaborate?
                                                         +-DLS


Basically I would like to get away from having a hardcoded representation of the names of filters inside the code. We now have 4 such filters, arp, rarp, ipv4 and ipv6 and you are adding 2 more arpmac and arpip. For ipv6 we would again need to add more. I think the names of the filters should be picked up from the XML and then in some way sorted and have them generate the rules

-j I-vnet0-mac
-p IPv4 -j I-vnet0-ipv4
-p ARP -j I-vnet0-arpmac
-p ARP -j I-vnet0-arpip
-p 0x8035 -j I-vnet0-rarp


in the right order. i.e., ipv4 before ipv6 before arpmac before arpip before rapr and 'arp' somewhere in between. This and later on an introduction of an action 'jump' or 'goto' with a target would then provide more flexibility for the user to build even more complex filters. I'll look into getting rid of the bit fields that I have been using so far and try to collect the names of filters. I guess they would have to be given an implicit 'priority' so they are ordered in that way above -- so maybe some of the filters are known to the system and have an implicit priority while others will have to be given a priority. Comments?

   Stefan

lab1.dls 226 # ebtables -t nat -L
Bridge table: nat

Bridge chain: PREROUTING, entries: 1, policy: ACCEPT
-i vnet0 -j libvirt-I-vnet0

Bridge chain: OUTPUT, entries: 0, policy: ACCEPT

Bridge chain: POSTROUTING, entries: 1, policy: ACCEPT
-o vnet0 -j libvirt-O-vnet0

Bridge chain: libvirt-I-vnet0, entries: 9, policy: ACCEPT
-j I-vnet0-mac
-p IPv4 -j I-vnet0-ipv4
-p ARP -j I-vnet0-arpmac
-p ARP -j I-vnet0-arpip
-p 0x8035 -j I-vnet0-rarp
-p 0x835 -j ACCEPT
-p IPv4 -j ACCEPT
-p ARP -j ACCEPT
-j DROP

Bridge chain: libvirt-O-vnet0, entries: 5, policy: ACCEPT
-p IPv4 -j O-vnet0-ipv4
-p 0x8035 -j O-vnet0-rarp
-p IPv4 -j ACCEPT
-p ARP -j ACCEPT
-j DROP

Bridge chain: I-vnet0-mac, entries: 1, policy: DROP
-s 54:0:0:0:0:1 -j RETURN

Bridge chain: I-vnet0-ipv4, entries: 5, policy: DROP
-p IPv4 --ip-src 10.0.0.1 -j RETURN
-p IPv4 --ip-src 0.0.0.0 --ip-proto udp --ip-sport 68 -j RETURN
-p IPv4 --ip-src 11.0.0.0/24 -j RETURN
-p IPv4 --ip-src 10.0.0.3 -j RETURN
-p IPv4 --ip-src 10.0.0.4 -j RETURN

Bridge chain: O-vnet0-ipv4, entries: 1, policy: DROP
-j ACCEPT

Bridge chain: I-vnet0-arpmac, entries: 1, policy: DROP
-p ARP --arp-mac-src 54:0:0:0:0:1 -j RETURN

Bridge chain: I-vnet0-arpip, entries: 5, policy: DROP
-p ARP --arp-ip-src 10.0.0.1 -j RETURN
-p ARP --arp-ip-src 0.0.0.0 -j RETURN
-p ARP --arp-ip-src 11.0.0.0/24 -j RETURN
-p ARP --arp-ip-src 10.0.0.3 -j RETURN
-p ARP --arp-ip-src 10.0.0.4 -j RETURN

Bridge chain: I-vnet0-rarp, entries: 1, policy: DROP
-p 0x8035 -s 54:0:0:0:0:1 -d Broadcast --arp-op Request_Reverse
--arp-ip-src 0.0.0.0 --arp-ip-dst 0.0.0.0 --arp-mac-src 54:0:0:0:0:1
--arp-mac-dst 54:0:0:0:0:1 -j ACCEPT

Bridge chain: O-vnet0-rarp, entries: 1, policy: DROP
-p 0x8035 -d Broadcast --arp-op Request_Reverse --arp-ip-src 0.0.0.0
--arp-ip-dst 0.0.0.0 --arp-mac-src 54:0:0:0:0:1 --arp-mac-dst 54:0:0:0:0:1
-j ACCEPT




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