Figure 8-7: The Routing Process A Routing decision 3. After selecting the best-match row the router sends the packet on to the next-hop router indicated in the best-match row-Next-Hop Router B in this example Send Packet out to Route IP AddressMetricNext-Hop NhR B Range Router 60.3xX B Best-Match Row 2 128.171.xx 2 B 8-26
8-26 Figure 8-7: The Routing Process • A Routing Decision – 3. After selecting the best-match row, the router sends the packet on to the next-hop router indicated in the best-match row—Next-Hop Router B in this example. Route IP Address Range Metric Next-Hop Router 1 60.3.x.x 9 B 2 128.171.x.x 2 B Best-Match Row Send Packet out to NHR B
B A More Detailed look at Routing Decisions
A More Detailed Look at Routing Decisions Box
Figure 8-8: Detailed Row-Matching algorithm Box Routing table IP Address Range Row Destination Mask 10.7.3.02552552550 Actually, the table does not really have an"IP Address Range column Instead it has two columns to indicate the ip address range Destination(an IP address ) and a mask 8-28
8-28 Figure 8-8: Detailed Row-Matching Algorithm • Routing Table IP Address Range Row Destination Mask … … … 1 10.7.3.0 255.255.255.0 … … … 2 … … … … … 3 … … … … … Box Actually, the table does not really have an “IP Address Range” column. Instead, it has two columns to indicate the IP address range: Destination (an IP address) and a mask
Figure 8-8: Detailed Row-Matching Algorithm Box 1. Basic Rule of Masking Information Bit Mask Bit 1100 Result 1000 Where mask bits are one the result gives the original IP address bits Where mask bits are zero. the result contains zeros 8-29
8-29 Figure 8-8: Detailed Row-Matching Algorithm • 1. Basic Rule of Masking – Information Bit 1 0 1 0 – Mask Bit 1 1 0 0 – Result 1 0 0 0 • Where mask bits are one, the result gives the original IP address bits • Where mask bits are zero, the result contains zeros Box
Figure 8-8: Detailed Row-Matching Algorithm Box 2. Example Address (partial) 1010101011001110 Mask 1111100000000000 Resu1七 1010100000000000 8-30
8-30 Figure 8-8: Detailed Row-Matching Algorithm • 2. Example – Address (partial) 10101010 11001110 – Mask 11111000 00000000 – Result 10101000 00000000 Box