IP Routing Reading Chapter 16 Fall 2004 FSU

IP Routing Reading: Chapter 16 Fall 2004 FSU CIS 5930 Internet Protocols 1

IP routing End system Intermediate system (Router) End system Transport TCP Network IP IP IP Data link and physical PPP Fall 2004 PPP IEEE 802. 3 FSU CIS 5930 Internet Protocols IEEE 802. 3 2

Networks and routers Connection to the other networks of the Internet Router B Router A Network 3: Ethernet (IEEE 802. 3) Network 2: PPP Network 4: Fast Ethernet Network 1: Token Ring (IEEE 802. 5) Network 5: Wireless LAN (IEEE 802. 11) Router C Fall 2004 FSU CIS 5930 Internet Protocols 3

Forwarding vs. routing • Forwarding – Given a packet, determining the next hop toward destination by consulting some routing table – Per packet behavior – In kernel • Routing – Collecting/exchanging topology and state information, computing shortest path to destinations, constructing routing table – Periodically or event driven – In user space (some routing daemon) Fall 2004 FSU CIS 5930 Internet Protocols 4

IP addresses • Class-based ones – A, B, C, D, E – Inferring network part from addresses • Classless one (CIDR) – Explicitly network mask – 192. 168. 152. 0/21 – 192. 168. 152. 0/255. 248. 0 Fall 2004 FSU CIS 5930 Internet Protocols 5

An example Connection to the other networks of the Internet Router B 10. 0. 0. 1 Router A 10. 0. 2. 1 10. 0. 1. 1 10. 0. 2. 2 10. 0. 3. 1 10. 0. 3. 2 10. 0. 3. 3 10. 0. 5. 2 10. 0. 5. 3 10. 0. 4. 1 10. 0. 4. 2 10. 0. 1. 4 10. 0. 4. 3 10. 0. 5. 1 10. 0. 1. 3 Router C Fall 2004 FSU CIS 5930 Internet Protocols 6

Routing table for Routing B Destination Network mask 10. 0. 3. 0 255. 0 eth 0 10. 0. 4. 0 255. 0 eth 1 10. 0. 5. 0 255. 0 10. 0. 2. 0 255. 0 0. 0 Fall 2004 Router 10. 0. 4. 3 Interface eth 1 ppp 0 10. 0. 2. 1 FSU CIS 5930 Internet Protocols ppp 0 7

Some concepts • Longest prefix matching – More specific entries are preferred • Routing cache – Most recently used routing entries – To speed up forwarding • Rule-based routing – A unified way to organize different routing tables – local (local router), main (general table), default (default routing entry) – Each with a priority Fall 2004 FSU CIS 5930 Internet Protocols 8

Implementation • Data structures – Routing rules – Routing tables – Routing cache • Functions – Forwarding lookup functions – Management functions Fall 2004 FSU CIS 5930 Internet Protocols 9

Routing rules fib_rule r_next r_clntref: 2 r_preference: 0 r_preference: 32766 r_table: RT_TABLE_LOCAL r_table: RT_TABLE_MAIN r_action: RTN_UNICAST r_dst_len: 0 . . . r_src_len: 0 r_src: 0 x 0 r_srcmask: 0 x 0 fib_rule r_dst: 0 x 0 r_next: 0 x 0 r_dstmask: 0 x 0 r_srcmap: 0 x 0 r_flags: 0 r_tos: 0 r_ifindex: 0 r_clntref: 2 r_preference: 32767 r_table: RT_TABLE_DEFAULT r_action: RTN_UNICAST r_ifname[. . . ]: ““ . . . r_dead: 0 Fall 2004 FSU CIS 5930 Internet Protocols 10

Functions • fib_lookup(rt_key, …) – Searching for matching rules – If found • Get the routing table (fib_get_table()) • Looking up an entry in the table (tb_lookup()) • rt_key structure – dst, src, iif, oif, tos, scope, etc Fall 2004 FSU CIS 5930 Internet Protocols 11

Routing tables fib_tables[255] 1 fib_table tb_id: 1 0 . . . fn_zone fz_next: 0 x 0 fib_node*[1] fz_hash fz_divisor: 1 fib_table fz_hashmask: 0 x 0 fz_order: 0 254 fib_table fz_mask: 0 tb_id: 254 tb_stamp tb_lookup() 16 fn_zone fz_next tb_insert() fz_hash tb_delete() fz_divisor: 16 tb_dump() fz_hashmask: 0 xf tb_flush() fz_order: 16 tb_get_info() fz_mask: 0 xffff fib_node*[16] tb_select_default() fn_hash fn_zones[33] fn_zone_list 24 fn_zone fz_next fib_node*[16] fz_hash fz_divisor: 16 255 Fall 2004 fib_table fz_hashmask: 0 xf tb_id: 255 fz_order: 24 . . . fz_mask: 0 xffffff FSU CIS 5930 Internet Protocols 12

Zone, node, and info fib_node*[16] 0 fib_node fn_next fn_info fn_key . . . fib_node fn_tos fn_type fib_info fn_scope next fn_state fib_info prev fib_treeref fib_node fib_clntref fib_dead 15 fib_flags fib_node fib_prefsrc fib_priority fib_metrics[. . . ] fib_info_list fib_info_cnt next prev: 0 x 0 ? ? ? . . . fib_nhs fib_nh nh_dev net_dev nh_flags nh_scope nh_oif nh_gw Fall 2004 FSU CIS 5930 Internet Protocols 13

Routing cache rtable rt_hash_table[] dst_entry rtable next 0 . . . rt_hash_bucket dev net_dev . . . neighbour rt_hash_bucket hh hh_cache chain input() lock 16 rt_hash_bucket output() dst_ops . . . rt_flags gc() rt_type check() rt_dst reroute() rt_src destroy() rt_iif negative_advice() rt_gateway link_failure() rt_key negative_advice() entries rt_spec_dst inet_peer Fall 2004 inet_peer FSU CIS 5930 Internet Protocols . . . 14

Forwarding functions • ip_route_input() – For handling incoming packet – Searching cache first, done if found – Depending on destination address • Multicast: ip_route_input_mc() • Otherwise: ip_route_input_slow() Fall 2004 FSU CIS 5930 Internet Protocols 15

Forwarding functions • ip_route_input_slow() – Sanity checking – FIB query by fib_lookup() – Depending on if local address • If local: dst. input <- ip_local_delivery() • Otherwise: – Making the outgoing interface is up – dst. Input <- ip_forward() – dst. Output <- ip_output() Fall 2004 FSU CIS 5930 Internet Protocols 16

Forwarding functions • ip_route_output() – For locally generated packets – Creating rt_key structure – Passing on to ip_route_output_key() • ip_route_output_key() – Searching routing cache – If not found • ip_route_output_slow() Fall 2004 FSU CIS 5930 Internet Protocols 17

Forwarding functions • ip_route_output_slow() – Searching routing table – Local vs. nonlocal • Local: ip_local_delivery() • Nonlocal: – Dst. output <- ip_ouput() – Entering the result into routing cache Fall 2004 FSU CIS 5930 Internet Protocols 18