Enterprise QoS Solution Reference Network Design Guide

Chapter 6 IPSec VPN QoS Design
Version 3.3
Figure 6-4 Anatomy of an IPSec-Encrypted G.729 Packet
G.729
60 Bytes
IP GRE
84 Bytes
IPSec ESP
Tunnel Mode
136 Bytes
IPSec
Hdr
ESP
Hdr
ESP
IV
GRE IP
Hdr
20
GRE IP
Hdr
GRE
4
GRE
IP
Hdr
20
IP
Hdr
20
IP
Hdr
UDP RTP Voice
Site-to-Site V3PN QoS Considerations
It is important to note that these bandwidth allocations are Layer 3 bandwidth requirements and do not
include Layer 2 overhead (which is media dependent). Therefore, Layer 2 overhead needs to be added
on top of the Layer 3 requirements in provisioning LLQ and CBWFQ bandwidth. This is illustrated in
Figure 6-5, where Ethernet overhead (Ethernet plus 802.1Q trunking) and Frame Relay overhead are
added and removed from the packet in transit.
Key Layer 2 overhead values are reiterated in Table 6-1.
8
12
RTP
RTP
ESP
Pad/NH
ESP
Auth
20 8 8 20 4 20 8 12 20 2-257 12
Table 6-1 Layer 2 Encapsulation Overhead
UDP
8
UDP
Encrypted
Authenticated
12
Enterprise QoS Solution Reference Network Design Guide
20
Voice
20
Voice
Layer 2 Encapsulation Overhead
Ethernet 14 bytes (+ 4 for 802.1Q)
Frame Relay 4 bytes (+ 4 for FRF.12)
MLP 10 bytes (+ 3 for MLP LFI)
ATM 5 bytes per 53-byte cell + cell padding (variable)
6-7