LAN FRAME FORMATS www.sorin-schwartz.com IEEE 802.2 - LLC (Logical - PowerPoint PPT Presentation

LAN FRAME FORMATS www.sorin-schwartz.com IEEE 802.2 - LLC (Logical link Control) ----- 1 ----- DSAP field (1byte) SSAP field (1byte) M DA 6 A X X X X X X U I X X X X X X U C SA 6 C LSB LSB ----- 2 L DSAP=P.ID 1 L S I = Group/Individual SAP C = Response/Command L A SSAP=P.ID 1 1 = Group SAP 1 = Response P C CONTROL 1-2 0 = Individual SAP 0 = Command 3 + DATA U = Universal (IEEE 802)/User defined SAP 1 = Universal SAP 0 = User SAP 3 + DATA X = Six bits used to define SAP codes 2 4 FCS BRS07 1

LAN FRAME FORMATS www.sorin-schwartz.com SNAP � SNAP "opens" the frame for five additional bytes, 1 ----- � the PIF = Protocol Information Field. ----- M DA 6 A SA 6 C � PIF has two fields: ----- 2 L - OUI - Organizationally Unique Identifier – 3 bytes DSAP=SNAP 1 S A SSAP=SNAP 1 L - globally administrated by IEEE 802.2 P L CONTROL 1 - OUI 00-00-00 is reserved for use in "special" cases. C OUI 3 (administrated by IETF - International Engineering Task Force) PIF P.ID 2 3 - P.ID - Protocol Identifier – 2 bytes + DATA - locally administrated by each organization having an OUI. 3 + DATA 2 FCS 4 BRS07 2

www.sorin-schwartz.com Routing Tables - Example: Class-less (CIDR) Environment prefix Network Prefix length RB p RA subNET 1 /23 p 10 xxxxxxx /25 /24 ISP 1 ISP 1 1 received ISP 2 a block /25 1 R8 received a /23 (=p) block /27 R1 2 /26 subNET2 2 /27 p 0011 xxxxx /27 ISP 3 1 /28 received subNET 3 a block R2 /25 /29 p 01 001 xxxx 2 /28 p /30 1 1 01 2 4 /31 R7 R3 101 2 3 host subNET 7 1 ISP 2 ISP 3 xxxx R5 1 2 3 subNET5 R4 /28 1 3 p 01 1110 xxx 2 /29 R6 HOST X p - 01 - 110 - 0101 2 subNET6 subNET 4 p 01 110 xxxx /28 p 01 01 xxxxx /27 BRS07 3

www.sorin-schwartz.com Routing Tables - Example: Class-less (CIDR) Environment RB RA subNET 1 RA p 10 xxxxxxx subNET 1 /25 RB ISP 1 1 received ISP 2 a block 1 R1 R8 R8 received a /23 (=p) block /27 R1 2 subNET2 subNET 2 2 R2 p 0011 xxxxx /27 ISP 3 1 received subNET 3 subNET 3 a block R2 R7 /25 p 01 001 xxxx 1 2 /28 subNET 7 R3 2 p 1 4 1 R6 1 01 3 2 4 1 R7 R3 R4 2 X 3 R5 101 2 3 2 subNET 6 1 3 subNET 7 1 subNET 4 subNET 5 xxxx R5 1 2 3 subNET5 R4 /28 1 3 p 01 1110 xxx 2 /29 R6 HOST X p - 01 - 110 - 0101 2 subNET6 subNET 4 p 01 110 xxxx /28 p 01 01 xxxxx /27 BRS07 4

www.sorin-schwartz.com Routing Tables - Example: Class-less (CIDR) Environment To destination Deliver RB Nr. of to Port - RIP tables do not include mask length hops RA subNET 1 router - OSPF tables do include mask length p 10 xxxxxxx /25 Initial table in Host X subNET 1 p 01 110 xxxx - X.1 0 4 1 R8 0.0.0.0 (default) R4 X.1 1 R1 2 subNET2 Initial table in R4 2 subNET p 0011 xxxxx /27 p 01 110 xxxx - R4.2 0 4 1 0.0.0.0 (default) R3 R4.1 1 subNET 3 R2 Initial table in R3 p 01 001 xxxx 2 /28 subNET p 01 001 xxxx - R3.1 0 p 3 1 1 01 2 0.0.0.0 (default) R2 R3.1 1 4 R7 R3 Initial table in R5 101 2 3 subNET p 01 1110 xxx - R5.3 0 5 subNET 7 1 xxxx R5 0.0.0.0 (default) R3 R5.1 1 1 2 3 Initial routing tables subNET5 R4 /28 1 3 p 01 1110 xxx 2 /29 R6 HOST X p - 01 - 110 - 0101 2 subNET6 subNET 4 p 01 110 xxxx /28 p 01 01 xxxxx /27 BRS07 5

LAYER 4 SWITCHING www.sorin-schwartz.com NETWORK ADDRESS PORT TRANSLATION client #2 Application #1 192.108.33.2 Net address NAPT Network server 205.123.22.8 192.108.33.6 PORT translating PORT 18.14.111.2 3000 1500 � NAPT allows the use of one single PORT client #8 PORT globally 21 2126 192.108.33.8 administrated IP address for multiple PORT 3130 simultaneously MyNET active users � NAPT allows changing of this Layer 4 PORT Layer 3 ADDRESS Layer 2 ADDRESS unique address without having to dest. source dest. source dest. source modify every client #2 21 3000 18.14.111.2 192.108.33.2 NAPT client #2 individual user’s IP to NAPT (blue) (yellow) (red) (yellow) address (CIDR environment) NAPT to 21 18.14.111.2 205.123.22.8 ... ... � NAPT identifies server (blue) (red) 1500 incoming packets based on their Layer server to 1500 21 205.123.22.8 18.14.111.2 ... ... 4 DESTINATION port NAPT (red) (blue) NAPT to 21 192.108.33.2 18.14.111.2 client #2 NAPT client #2 (yellow) (blue) (yellow) (red) 3000 BRS07 6