Recall the CFG G4 that we gave in Example 2.4. For convenience, let’s rename its variables with single letters as follows. E → E + T | T T → T x F | F F → (E) | a Give parse trees and derivations for each string. a. a b. a+a c. a+a+a

Suppose a router has built up the routing table shown in the table. subnet number 128.96.39.00 28.96.39.128 128.96.40.00 192.4.153.0 default) subnet mask 255.255.255.128 255.255.255.128 255.255.255.128 255.255.255.192 nexthop interface 0 interface 1 r2 r3 r4. the router can deliver packets directly over interfaces 0 and 1, or it can forward packets to routers r2, r3, or r4. describe what the router does with a packet addressed to each of the following destinations: (a) 128.96.39.10 (b) 128.96.40.12 (c) 128.96.40.151 (d) 192.4.153.17 (e) 192.4.153.90