Moving packets. Moving datagrams. Suppose host A want to send IP to host B. Host A wants to send to host E. Generalized forwarding and SDN

Transcription

1 Mving packets Generalized frwarding and SDN Mving datagrams 1. Surce hst fills in its address Data field is filled with paylad. CS242 Cmputer Netwrks and addresses destinatin address. Department f Cmputer Science Wellesley Cllege Nw what? Generalized frwarding Suppse hst A want t send t hst B Hst A cnsults its frwarding table and discvers B's address matches its wn and that the number f hps is 1: A and B are n the same subnet. Hst A wants t send t hst E Hst A again cnsults its frwarding table and discvers E is n a different subset 2 hps away. Hst A als learns that ruter interface is the first hp. Hst A then passes the datagram t the link-layer prtcl fr that interface Generalized frwarding Generalized frwarding

2 Frwarding table in ruter The datagram is nw in the ruter whse jb it is t mve it tward its final destinatin (E). The ruter's table indicates that the datagram shuld be frwarded t ruter interface and that E is 1 hp away. And that s the way it was As illustrated, an Internet ruter s frwarding decisin was based slely n a packet s destinatin. Hwever, NAT bxes rewrite addresses and prt numbers; firewalls blck based n headerfields; lad-balancers frward packets requesting a given service. The list ges n. Generalized frwarding Generalized frwarding A mre general match-plus-actin Generalize frwarding In the previus example, frwarding cnsisted f tw steps: (i) Lkup address (match); (ii) set switching fabric t specified prt (actin). We cnsider a mre general match-plusactin paradigm where match can be made ver multiple header fields assciated with different prtcls.* *This will invlve bth layer 3 ruters and layer 2 switch. We refer fr bth simply as packet switches. Generalized frwarding Generalized frwarding

3 Flw table entries Packet matching fields* A set f header field values t which the incming packet will be matched. A set f cunters that are updated as packets are matched. These might include number f packets matched and time since entry was updated. A set f actins t be taken when a packet is matched, such as, frward, drp, make and send cpies, rewrite header fields. Ingress Prt Src Mac Dst MAC Eth Type Link Layer VLAN ID Src VLAN Pri Dst Prt Netwrk Layer TP TOS *OpenFlw 1.0 flw table; rather brazenly defies ur layering principle. TCP/UDP TCP/UDP Src Prt Dst Prt Transprt Layer Generalized frwarding Generalized frwarding Actins Simple frwarding* Frwarding. A packet can be frward t a particular prt, bradcast ver all prts, r multi-caste ver selected prts. Drpping. A flw entry with n actin indicates that a matched packet shuld be drpped. Mdify-field. Values in all but Ingress and Prtcl fields may be rewritten befre packet is frwarded. *Packets frm h5, h6 are t be frward frm s3 t s1, and then frm s1 t s2. Generalized frwarding Generalized frwarding

4 s1 Flw table s3 Flw table Actin Actin Ingress Prt = 1; Src = 10.3.*.*; Dst = 10.2.*.* Frward(4) Src = 10.3.*.*; Dst = 10.2.*.* Frward(3) *Packets frm h5, h6 are t be frward frm s3 t s1, and then frm s1 t s2. Generalized frwarding *Packets frm h5, h6 are t be frward frm s3 t s1, and then frm s1 t s2. Generalized frwarding s2 Flw table Lad balancing* Ingress prt = 2; Dst = Ingress prt = 2; Dst = Actin Frward(3) Frward(4) *Packets frm h5, h6 are t be frward frm s3 t s1, and then frm s1 t s2. Generalized frwarding *Datagrams frm h3 are t be frwarded ver the direct link between s2 t s1. Generalized frwarding

5 s2 Flw table Firewalling* Ingress prt = 3; Dst = 10.1.*.* Ingress prt = 4; Dst = 10.1.*.* Actin Frward(2) Frward(1) *Datagrams frm h3 are t be frwarded ver the direct link between s2 t s1. Generalized frwarding *Packet switch s2 wants nly t receive traffic sent frm hsts attached t s3. Generalized frwarding s2 Flw table Src = 10.3.*.*; Dst = Src = 10.3.*.*; Dst = Actin Frward(3) Frward(4) *Packet switch s2 wants nly t receive traffic sent frm hsts attached t s3. Generalized frwarding