Ruijie RG-S2900G-E Series - Page 774

Configuration Guide Access Control List Configuration
In the figure above, the meaning of each letter and the value of offset are shown below:
Letter
Meaning
Offset
Letter
Meaning
Offset
A
Destination MAC
0
O
TTL field
34
B
Source MAC
6
P
Protocol ID
35
C
VLAN tag field
12
Q
IP checksum
36
D
Data frame length field
14
R
Source IP address
38
E
DSAP field
18
S
Destination IP address
42
F
SSAP field
19
T
TCP source port
46
G
Ctrl field
20
U
TCP destination port
48
H
Org Code field
21
V
Sequential number
50
I
Encapsulated data type
24
W
Confirmation field
54
J
IP version No.
26
XY
IP header length and
reservation bits
58
K
TOS field
27
Z
Reservation bit and flags bit
59
L
IP packet length
28
a
Windows size field
60
M
ID
30
b
Others
62
N
Flags field
32
As shown in the above table, the offset of each field is it offset in the SNAP+tag 802.3 data frame. In
the user custom access control list, the user can use two parameters, the rule mask and offset, to
abstract any byte from the first 80 bytes of the data frame, and then compare it with the user defined
rule to filter the matched data frame for corresponding processing. The user defined rule can be some
fixed attributes of the data. For example, the user wants to filter all the TCP messages by defining the
rule as “06”, rule mask as “FF” and offset as 35. Here, the rule mask and offset work together to
abstract the contents of the TCP protocol ID field in the received data frame, and compare it with the
rule to filter all TCP messages.