29.2
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In our udpcksum program, common error
replies are an ICMP "port unreachable" (the destination is not
running a name server) or an ICMP "host unreachable." In either
case, we need not wait for a timeout of our udp_read in
Figure 29.10 because
the ICMP error is essentially a reply to our DNS query. Modify the
program to catch these ICMP errors.
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