Cisco Headend Digital Broadband Delivery System インストールガイド
Chapter 1 SR i4.2.2 DVD Pre-Upgrade Procedures
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4036631 Rev B
Check the Time to Live Parameter
The number of "hops" refers to the number of routers a single packet of data
traverses on its way to its destination. In the case of router failure or network
misconfiguration, a packet of data can theoretically exist in an endless loop, never
reaching its destination and never being discarded by the system.
To prevent data from existing in an endless loop, IP packets of data contain a Time
to Live (TTL) parameter that decrements by 1 each time that packet of data navigates
a router. This protocol is designed to discard the packet whenever the TTL
parameter reaches 0.
We use a default TTL parameter of 10 for IP multicast packets that are generated by
the DNCS; there are no known DBDS systems that are configured to require more
than 10 hops for a packet of data to reach its destination.
In this procedure, you will "probe" each Cable Modem Termination System (CMTS)
on the network and analyze the number of hops required for a packet of data to
reach the CMTS. To do this, you will query the database to obtain the IP address of
each CMTS. Then, you will run the traceroute command against every CMTS and
count the number of hops. If the traceroute command reveals that data requires 8 or
more hops to reach any CMTS, you will then modify the TTL parameter in the
/export/home/dncs/.profile file on the DNCS.
traverses on its way to its destination. In the case of router failure or network
misconfiguration, a packet of data can theoretically exist in an endless loop, never
reaching its destination and never being discarded by the system.
To prevent data from existing in an endless loop, IP packets of data contain a Time
to Live (TTL) parameter that decrements by 1 each time that packet of data navigates
a router. This protocol is designed to discard the packet whenever the TTL
parameter reaches 0.
We use a default TTL parameter of 10 for IP multicast packets that are generated by
the DNCS; there are no known DBDS systems that are configured to require more
than 10 hops for a packet of data to reach its destination.
In this procedure, you will "probe" each Cable Modem Termination System (CMTS)
on the network and analyze the number of hops required for a packet of data to
reach the CMTS. To do this, you will query the database to obtain the IP address of
each CMTS. Then, you will run the traceroute command against every CMTS and
count the number of hops. If the traceroute command reveals that data requires 8 or
more hops to reach any CMTS, you will then modify the TTL parameter in the
/export/home/dncs/.profile file on the DNCS.
Obtaining the CMTS IP Addresses
Follow these instructions to query the database regarding the IP address of each
CMTS.
Note: To be certain that the IP address of each CMTS has been properly entered into
the database, you may want to cross-reference any IP addresses returned from the
database against the documentation that accompanied the CMTS.
1 From an xterm window on the DNCS, type dbaccess dncsdb - and then press
CMTS.
Note: To be certain that the IP address of each CMTS has been properly entered into
the database, you may want to cross-reference any IP addresses returned from the
database against the documentation that accompanied the CMTS.
1 From an xterm window on the DNCS, type dbaccess dncsdb - and then press
Enter. The system opens the DNCS database.
2 Type select * from cmts; and then press Enter. The system displays the rows in
the cmts table.
id name ipaddr ipaddr2
2 vod4CiscoCMTS
id name ipaddr ipaddr2
2 vod4CiscoCMTS
192.168.201.201
1 row(s) retrieved.