1044 BigIron RX Series Configuration Guide
53-1002253-01
Configuring sFlow
39
ACL-based inbound sFlow
This feature is available only for IPv4.
IPv4 ACL traffic samples can be sent to an sFlow collector. The data matching an ACL clause can be
collected to observe traffic flow patterns and quantities between a set of switches and routers. To
accommodate collecting sFlow through standard procedures and using ACL-filtered traffic, Brocade
created the Proprietary Tag Type 1991 that encapsulates the sFlow samples obtained through
ACL-based sFlow and separates them from the sequence flow of other sFlow samples. Figure 1
shows the format of an sFlow packet, which illustrates the differences between a standard sFlow
payload and an ACL-based payload.
As shown in Figure 1, sFlow is carried in a UDP packet. Within the UDP packet, the sFlow contents
are carried in individual samples that are identified by a Tag Type and a Length variable. The
standard values for the Tag Types are 1 = sampled packet and 2 = counter sample. The length
variable describes the length of the sample. Within the sample are other variables including the
Sequence number and the Source ID.
Brocade has introduced the proprietary Tag Type 1991 to identify ACL-based sFlow samples. For
these samples, standard Tag Type 1 samples collected using ACL-based Inbound sFlow are
encapsulated in a Tag Type 1991 sample. The length variable identifies the entire length of the Tag
Type 1991 sample including the encapsulated Tag Type 1 sample. The encapsulated sample has a
length variable of its own that only identifies the length of that sample.
The Tag Type 1991 samples are sequenced separately from the unencapsulated Tag Type 1
samples. For instance in the packet detail described in the "Sequence Flow for sFlow Records" in
Figure 1, the top sFlow record with Tag Type 1 begins with the sequence number 1. The next sFlow
record is of Tag Type 1991 which indicates that the sample contained is from ACL-based sFlow.
Encapsulated within this ACL-based sFlow sample is an sFlow sample record of Tag Type 1. The
ACL-based sFlow sample (which contains the Type 1 sample) is followed by an unencapsulated Tag
Type 1 sFlow sample. That unencapsulated Tag Type 1 sFlow sample follows the sequence
numbering of the first unencapsulated Tag Type 1 sFlow sample which gives it a sequence number
of 2.
This is useful in cases where an sFlow collector does not recognize Tag Type 1991. In these
situations, the Tag Type 1991 samples can be ignored without disrupting the sFlow sequence
numbers. It is also useful for identifying samples obtained using ACL-based sFlow that you might
want to perform other processes.
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