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Question 90

There are three servers in the pool: 172.16.20.1, 172.16.20.2, and 172.16.20.3, with the virtual IP address 10.0.20.88.

A user CANNOT connect to an HTTP application. To understand the problem and find a solution, the LTM Specialist runs two concurrent traces on the LTM device, with the following results:

Trace on client side:

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on 0.0, link-type EN10MB (Ethernet), capture size 96 bytes

22:22:07.423759 IP 172.16.20.100.53875 > 10.0.20.88.80: S 998346084:998346084(0) win 5840

22:22:07.424056 IP 10.0.20.88.80 > 172.16.20.100.53875: S 4671780:4671780(0) ack 998346085 win 4380

2392362490 67942058,sackOK,eol>

22:22:07.424776 IP 172.16.20.100.53875 > 10.0.20.88.80: . ack 1 win 365

22:22:07.424790 IP 172.16.20.100.53875 > 10.0.20.88.80: P 1:149(148) ack 1 win 365

22:22:07.424891 IP 10.0.20.88.80 > 172.16.20.100.53875: . ack 149 win 4528

22:22:12.024850 IP 10.0.20.88.80 > 172.16.20.100.53875: R 1:1(0) ack 149 win 4528

6 packets captured

6 packets received by filter

0 packets dropped by kernel

Trace on server side:

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on internal, link-type EN10MB (Ethernet), capture size 96 bytes

22:22:07.424881 IP 172.16.20.100.53875 > 172.16.20.2.80: S 51116678:51116678(0) win 4380

0,sackOK,eol>

22:22:08.424893 IP 172.16.20.100.53875 > 172.16.20.2.80: S 51116678:51116678(0) win 4380

0,sackOK,eol>

22:22:09.625082 IP 172.16.20.100.53875 > 172.16.20.2.80: S 51116678:51116678(0) win 4380

0,sackOK,eol>

22:22:10.825194 IP 172.16.20.100.53875 > 172.16.20.2.80: S 51116678:51116678(0) win 4380

4 packets captured

4 packets received by filter

0 packets dropped by kernel

What should the LTM Specialist do to solve the problem?

    Correct Answer: D

    The problem described indicates that the client can connect to the virtual server IP (10.0.20.88:80), but the requests from the client are not being forwarded to the pool members correctly. This is evident from the server-side trace, which shows that the server does not respond to SYN packets sent to it, likely because it does not recognize the source IP address (172.16.20.100) as a valid return path. Configuring the virtual server to use SNAT (Source Network Address Translation) will ensure that the source IP of the client's packets is translated to an IP that the server recognizes, allowing for proper communication between the client, the LTM, and the server.

Discussion
GVKDOption: D

D - Correct