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Cisco WAAS: Getting pass-through in the logs of optimized traffic flow




WAAS devices optimise and compress traffic flows between two points. For this optimization to work the end point WAE devices should be in sync and using same parameters. The Edge WAE is a client-side, file-caching device that serves client requests at remote sites and branch offices. The device is deployed at each branch office or remote campus, replacing file and print servers and giving local clients fast, near-LAN read and write access to a cached view of the centralized storage. The Core WAE is a server-side component that resides at the data center and connects directly to one or more file servers or network-attached storage (NAS). Core WAEs are placed between the file servers at the data center and the WAN connecting the data center to the enterprise's remote sites and branch offices.



Bypass and Pass-through traffic

Bypass traffic are the traffic which WAAS bypasses and returns back to the Router. The reason for bypassing this traffic could be different - static bypass list configured on WAAS or some overload conditions on WAAS itself. WCCP Return Method is used to return this traffic back to the router. Bypass is a function of WCCP that allows a WAE to return redirected traffic that it does not optimized back to the WCCP server.


Pass Through traffic, unlike bypass traffic are accepted by WAAS. WAAS will process the traffic and does Application Traffic Policy Look up  to determine whether it can optimize the traffic. If it cannot be optimized, WAAS will simply pass-through the traffic.This Pass-through traffic make use of the 'Egress Method' configured on WAAS to send it back to the router, similar to any other optimized traffic flow. So depending upon the Egress Method configured, it can be either of IP Forwarding, WCCP GRE Return or Generic GRE Return.



When entering the command "sh statistics connection optimized" you are getting lots of active pass-through flows.


WAAS#sh statistics connection optimized
Current Active Optimized Flows:                      3
   Current Active Optimized TCP Plus Flows:          3
   Current Active Optimized TCP Only Flows:          0
   Current Active Optimized TCP Preposition Flows:   0
Current Active Auto-Discovery Flows:                 3
Current Reserved Flows:                              40
Current Active Pass-Through Flows:                   34

Historical Flows:                                    207
D:DRE,L:LZ,T:TCP Optimization RR:Total Reduction Ratio
ConnID        Source IP:Port          Dest IP:Port            PeerID                Accel RR
52362       a.b.c.d:61679           p.q.r.s:257                d4:8c:b5:4e:0d:1c TDL   00.0%
52363        p.q.r.s:59825         a.b.c.d:18192              d4:8c:b5:4e:0d:1c TDL   00.0%
52365        p.q.r.s:60189         h.i.j.k:18192                d4:8c:b5:4e:0d:1c TDL   00.0%



To view the connections in detail issue command "sh statistic connections | in <ip addr>". You can also use command "show stat connection pass-through ".


WAAS#sh statistics connection | i 10.24.177.     N/A               PT Asymmetric     N/A               PT Asymmetric     N/A               PT Asymmetric      N/A               PT In Progress     N/A               PT Asymmetric     N/A               PT In Progress

This output shows the connections between the hosts as Pass-through Asymmetric.



The reason for these pass-through asymmetric traffic flows is asymmetric routing between the end points. Remember that WAAS will not optimize the asymmetric traffic flow. Checking the routing path flow between the hosts will help identify the asymmetric routing issue.



Related Information

WAAS Pass through traffic
Differences between bypass traffic and pass-through traffic in WAAS


Version history
Revision #:
2 of 2
Last update:
‎08-29-2017 05:44 AM
Updated by: