Port Features
Page 44
7750 SR OS Interface Configuration Guide
Cisco HDLC
Cisco HDLC (cHDLC) is an encapsulation protocol for information transfer. It is a bit-oriented
synchronous data-link layer protocol that specifies a data encapsulation method on synchronous
serial links using frame characters and checksums.
cHDLC monitors line status on a serial interface by exchanging keepalive request messages with
peer network devices. It also allows routers to discover IP addresses of neighbors by exchanging
Serial Link Address Resolution Protocol (SLARP) (see
) address-request and
address-response messages with peer network devices.
The basic frame structure of a cHDLC frame is shown in
. This frame structure is similar
to PPP in an HDLC-link frame (RFC 1662,
PPP in HDLC-like Framing
). The differences to PPP
in and HDLC-like frames are in the values used in the address, control, and protocol fields.
•
Address field — The values of the address field include: 0x0F (unicast), 0x8F (broadcast).
•
Control field — The control field is a
l
ways set to value 0x00.
•
Protocol field — The following values are supported for the protocol field:
•
Information field — The length of the information field is in the range of 0 to 9Kbytes.
•
FCS field — The FCS field can assume a 16-bit or 32-bit value. The default is 16-bits for
ports with a speed equal to or lower than OC-3, and 32-bits for all other ports. The FCS for
cHDLC is calculated in the same manner and same polynomial as PPP.
Table 10: cHDLC I-Frame
Flag
Address
Control
Protocol
Information
Field
FCS
0x7E
0x0F/0x8F
0x00
—
—
16/32 bits
Table 11: cHDLC Protocol Fields
Protocol
Field Value
IP
0x0800
Cisco SLARP
0x8035
ISO CLNP/ISO ES-IS DSAP/SSAP1
0xFEFE
Summary of Contents for 7750 SR OS
Page 6: ...Page 6 7750 SR OS Interface Configuration Guide Table of Contents ...
Page 8: ...Page 8 7750 SR OS Interface Configuration Guide List of Tables ...
Page 10: ...Page 10 7750 SR OS Interface Configuration Guide List of Figures ...
Page 14: ...Preface Page 14 7750 SR OS Interface Configuration Guide ...
Page 16: ...Getting Started Page 16 7750 SR OS Interface Configuration Guide ...
Page 184: ...Card MDA and Port Command Reference Page 184 7750 SR OS Interface Configuration Guide ...
Page 438: ...Debug Commands Page 438 7750 SR OS Interface Configuration Guide ...
Page 444: ...Index Page 444 7750 SR OS Interface Configuration ...