Hi,
Is there a way to have the xymon client bind to a specific IP or interface? I have more than one interface on a machine and I am getting ghost reports because I setup xymon for eth0:0 instead of eth0.
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On 6 June 2017 at 00:13, Frank <ve2cii at canasoft.net> wrote:
Hi,Is there a way to have the xymon client bind to a specific IP or interface? I have more than one interface on a machine and I am getting ghost reports because I setup xymon for eth0:0 instead of eth0.
Based on the eth0:0 interface name, I assume you're using Linux . Under Linux you can use the routing table to nudge the kernel towards using a particular IP address you specify, by using the "src" parameter when adding a route. By default, the kernel chooses the source IP address based on a route table lookup of the destination. So you could add a route to your Xymon server that specifies the use of a specific src IP you want like so:
ip route add <xymsrv IP> dev eth0 src <eth0:0 IP>
As is normal for route lookups, the selection of the route with the "src" specified, is determined by the destination IP address, regardless of the process making the request or the protocol used. This means "ssh <xymon IP>" or "wget <xymon IP>" would also have the eth0:0 IP as their source, which may or may not be what you want.
Instead of using routing tricks, you could use iptables and can setup a source NAT (SNAT) rule for the traffic you're interested in, to "NAT" to the alternate IP address. For example, use a rule that only matches TCP/1984, which would change the source IP as it egresses the server, outbound on that port. Or, you could use the "owner" module to specify the "xymon" user, so that only the Xymon client traffic uses the alternative IP address. Or a combination of these.
Actually, it's slightly more complicated than that, because "SNAT" only operates in the nat/POSTROUTING, and "owner" only operates in the mangle/OUTPUT chain, you have to use "owner" to mark packets and then use "SNAT" to modify packets that have been so marked. For example, the following tags packets from processes run as the xymon user, but only when the destination port is 1984, and then performs the SNAT on the matched packets:
iptables -t mangle -A OUTPUT -p tcp -m owner --uid-owner xymon -m tcp --dport 1984 -j MARK --set-mark 0xdeadbeef iptables -t nat -A POSTROUTING -o eth0 -m mark --mark 0xdeadbeef -j SNAT --to-source <eth0:0 IP>
However, it would be nicer if the Xymon client could be told to bind to a particular IP address (or interface name).
J
Hi,
Thank you for your input. It is good to know but I think it is a bit overkill. Right now the system is working perfectly, and I just used the name associated with eth0:0. But it would be nice if xymon was able to bind to the IP. Oh yes I am using linux.
On 6/8/17 2:04 AM, Jeremy Laidman wrote:
On 6 June 2017 at 00:13, Frank <ve2cii at canasoft.net <mailto:ve2cii at canasoft.net>> wrote:
Hi, Is there a way to have the xymon client bind to a specific IP or interface? I have more than one interface on a machine and I am getting ghost reports because I setup xymon for eth0:0 instead of eth0.Based on the eth0:0 interface name, I assume you're using Linux . Under Linux you can use the routing table to nudge the kernel towards using a particular IP address you specify, by using the "src" parameter when adding a route. By default, the kernel chooses the source IP address based on a route table lookup of the destination. So you could add a route to your Xymon server that specifies the use of a specific src IP you want like so:
ip route add <xymsrv IP> dev eth0 src <eth0:0 IP>
As is normal for route lookups, the selection of the route with the "src" specified, is determined by the destination IP address, regardless of the process making the request or the protocol used. This means "ssh <xymon IP>" or "wget <xymon IP>" would also have the eth0:0 IP as their source, which may or may not be what you want.
Instead of using routing tricks, you could use iptables and can setup a source NAT (SNAT) rule for the traffic you're interested in, to "NAT" to the alternate IP address. For example, use a rule that only matches TCP/1984, which would change the source IP as it egresses the server, outbound on that port. Or, you could use the "owner" module to specify the "xymon" user, so that only the Xymon client traffic uses the alternative IP address. Or a combination of these.
Actually, it's slightly more complicated than that, because "SNAT" only operates in the nat/POSTROUTING, and "owner" only operates in the mangle/OUTPUT chain, you have to use "owner" to mark packets and then use "SNAT" to modify packets that have been so marked. For example, the following tags packets from processes run as the xymon user, but only when the destination port is 1984, and then performs the SNAT on the matched packets:
iptables -t mangle -A OUTPUT -p tcp -m owner --uid-owner xymon -m tcp --dport 1984 -j MARK --set-mark 0xdeadbeef iptables -t nat -A POSTROUTING -o eth0 -m mark --mark 0xdeadbeef -j SNAT --to-source <eth0:0 IP>
However, it would be nicer if the Xymon client could be told to bind to a particular IP address (or interface name).
J
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sysadm cronomagic.com/gemstelecom.com e-mail ve2cii at canasoft.net
POWERED BY LINUX
participants (2)
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jlaidman＠rebel-it.com.au
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ve2cii＠canasoft.net