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--- cluster:102 [2011/06/29 13:55]
hmeij created
+++ cluster:102 [2011/06/29 15:29]
hmeij
@@ Line 5: / Line 5: @@
 ==== NAT Story, part 2 ====
+Writing this up so I will remember what I did, and why.  Basic problem is this: How do you make a filesystem in a public VLAN available on a private network?  One solution is to work with Network Address Translation, or NAT in short.  More information at [[http://en.wikipedia.org/wiki/Network_address_translation|http://en.wikipedia.org/wiki/Network_address_translation]]
+We have a storage device which we refer to as flexstorage.wesleyan.edu which serves up a file system on login node petaltail.
+<code>
+[root@petaltail ~]# host flexstorage
+flexstorage.wesleyan.edu has address 129.133.24.81
+[root@petaltail ~]# df -h /home/dlbgroup
+Filesystem            Size  Used Avail Use% Mounted on
+flexstorage.wesleyan.edu:/share/dlbgroup
+G  588G  413G  59% /home/dlbgroup
+</code>
+Host petaltail has the following interfaces.  The file system in question is mounted on host petaltail as VLAN 1 can reach VLAN 24.
+<code>
+eth0      Link encap:Ethernet  HWaddr 00:18:8B:51:FA:42
+          inet addr:192.168.1.217  Bcast:192.168.255.255  Mask:255.255.0.0
+eth1      Link encap:Ethernet  HWaddr 00:18:8B:51:FA:44
+          inet addr:10.10.100.217  Bcast:10.10.255.255  Mask:255.255.0.0
+eth2      Link encap:Ethernet  HWaddr 00:15:17:80:8D:F2
+          inet addr:129.133.1.225  Bcast:129.133.1.255  Mask:255.255.255.0
+eth3      Link encap:Ethernet  HWaddr 00:15:17:80:8D:F3
+          inet addr:192.168.2.2  Bcast:192.168.2.255  Mask:255.255.255.0
+</code>
+But a compute node on our cluster, for example node b1, has the following interfaces, all private
+<code>
+eth0      Link encap:Ethernet  HWaddr 00:13:D3:F2:C8:EC
+          inet addr:192.168.1.7  Bcast:192.168.255.255  Mask:255.255.0.0
+eth1      Link encap:Ethernet  HWaddr 00:13:D3:F2:C8:ED
+          inet addr:10.10.100.7  Bcast:10.10.255.255  Mask:255.255.0.0
+</code>
+So in order to for the compute node b1 to reach the flexstorage server we need to use NAT rules and define a path/route.  First we start on petaltail and edit the iptables file and add a "nat filter" masquerade/post routing directives and in the "filter filter" set up a rule connecting eth1 and eth2.
+<code>
+*nat
+# fss public to 10.10
+-A POSTROUTING -o eth2 -j MASQUERADE
+COMMIT
+*filter
+# fss public via 10.10
+-A FORWARD -i eth1 -o eth2 -m state --state RELATED,ESTABLISHED -j ACCEPT
+...
+COMMIT
+</code>
+Next, on the compute nodes we need to add routing path and then mount the file system (using an IP because there is no name resolving).  These commands are stuck in /etc/rc.local for persistence.
+<code>
+</code>
 \\
 **[[cluster:0|Back]]**

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