Multicast Routing

http://www.cymru.com/Documents/Cisco/multicast-router.txt


@(#)multicast routing howto 04 AUG 1997 Rob Thomas robt@cymru.com
How to setup a router to route multicast packets
Multicast is a UDP-based protocol which literally delivers packets from one
host to many. If abused, it can be made to deliver from many hosts to
many hosts to many hosts to many hosts... This is why it's important to
setup multicasting routing on the routers in a sane manner.
1. First, enable the global multicast routing parameter by:
!
ip multicast-routing
!
This can be disabled, if you so choose, by doing:
!
no ip multicast-routing
!
2. Next, select your style of multicasting. I chose PIM (Protocol-
Independent Multicast) for the following reasons:
- PIM works with all existing multicast routing protocols.
- PIM has two modes (dense & sparse) which gives me some freedom at
configuration time.
You could also choose from IGMP (Internet Group Management Protocol,
which is good for large WANs) or DVMRP (Distance Vector Multicast
Routing Protocol, which is slightly unsupported). However, be aware
that Cisco only tacitly supports DVMRP. To use DVMRP with a Cisco
router, you need to point your Cisco to a router that DOES support
DVMRP directly.
Of the two PIM choices, I went with dense mode. Here are the differences:
- Dense mode: When the router receives a multicast packet, the router
sends the packet out of all interfaces except for the interface from
whence the packet originated. If the router discovers that a certain
interface has no multicast recipients, it sends a "prune" message back
to the sender stating that there is no need to send messages to that
interface/subnet/link/host.
- Sparse mode: In sparse mode, it is assumed that no host wants multi-
cast packets unless the host specifically asks for it. So, instead
of the shotgun approach of dense mode, one router becomes the central
hub. This central hub logs all hosts that wish to receive multicast.
Further multicast packets are sent only to those hosts.
Seeing as how we only have two routers, I did not want one router to be
burdened with the list of multicast hosts (especially since practically
ALL of our hosts "want" multicast). Additionally, I did not want to
spend time fudging entries in the multicast recipient list.
So, to configure for PIM dense mode multicast routing:
!
interface ethernet 0
ip pim dense-mode
!
interface ethernet 1
ip pim dense-mode
!
Obviously, all involved routers should be speaking the same lingo. Thus,
routerA is configured the same as routerB.
3. Next, you need to set the multicast threshold. This is the BIG TRICK[tm]
to multicast routing. In a nutshell, every multicast packet has a TTL.
That's basic to all IP. By setting the multicast threshold on a given
router interface, you create a hurdle. If the packet's TTL is higher
than the multicast threshold, the packet may pass. If the packet's TTL
is LOWER than the multicast threshold, the packet is stopped (actually,
it is bounced with an ICMP message, but that's for another "howto" ;-).
This is how one prevents multicast packets from careening out into the
great 'Net. The range for multicast threshold is 0 to 255, with 0
meaning all packets may pass (well, *almost* all) and 255 meaning
virtually no packets may pass. On the routerB router, I set up the
multicast threshold at a comfortable 1 (because this is an internal
router). The multicast threshold on the interface leading to the
Internet on routerA should be set at 255 (if, in fact, multicast is
enabled on the interface at all).
!
interface ethernet 0
ip multicast-threshold 1
!
interface ethernet 1
ip multicast-threshold 1
!
And you're set!
4. It's probably a VERY good idea at this point to save your config. I
choose to save off to tftp (in case my NVRAM gets scrammed), but you
can choose your own danger here. At the least, you should copy your
running-config to your saved config.
router#copy running-config startup-config
Enjoy!
Questions/comments/bugs to: robt@cymru.com
Famous Unix quotes: "You are not expected to understand this."
-- From the original comments in the source code for Version 7's
process scheduling algorithm.
Rob Thomas, robt@cymru.com
http://www.enteract.com/~robt

Migration from GroupWise to Exchange

I have just a few users and the only data available is the "cache mode" copy on a laptop.

Search Results Page: "Instructions on exporting mail to a PST file from GroupWise using Outlook."

-Install the GroupWise Client.
-Install the Outlook 2002 Client.
-Load GroupWise Client and login as the user.
-Launch Outlook (this will connect to the GroupWise account that you are currently logged into).

Opening Attachments Blocked by the Microsoft Outlook E-mail Security Update:
"Opening .exe Attachments with the Outlook E-mail Security Update"

Allow the user to use a registry key to open up access to blocked attachments. (Always make a backup before editing the registry.) To use this key: Run Regedit, and go to this key:

HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Security

(change 10.0 to 9.0 for Outlook 2000 SP3 or to 11.0 for Outlook 2003) Under that key, add a new string value named Level1Remove. For the value for Level1Remove, enter a semicolon-delimited list of file extensions. For example, entering this: .mdb;.urlwould unblock Microsoft Access files and Internet shortcuts. Note that the use of a leading dot was not previously required, however, new security patches may require it. If you are using "mdb;url" format and extensions are blocked, add a dot to each extension. Note also that there is not a space between extensions. If you are using this registry entry, a glance at Help About Microsoft Outlook will show Security Mode: User Controlled above the license information. See OL2002 You Cannot Open Attachments for more information on this registry entry. To force users to save *.zip files to the hard drive before opening, add .zip to the extensions step 3. See How to configure Outlook to block additional attachment file name extensions for more information. If you prefer not to edit the registry directly, you can use one of these tools to make the change; not all support both Outlook 2002 and 2000:

Cisco::Tip::Reload in X

"reload in x" and "reload cancel"
When making configuration changes remotely that you think might disconnect you if you make a mistake, setup an automatic reboot in a few minutes, make the change, if you screw up and get disconnected, it will restart with the old config. After making a successful change, write the config and then cancel the restart.

The following example reloads the software on the router in 10 minutes:
Router# reload in 10

Router# Reload scheduled for 11:57:08 PDT Fri Apr 21 1996 (in 10 minutes)
Proceed with reload? [confirm]
The following example reloads the software on the router at 1:00 p.m. today:
Router# reload at 13:00

Router# Reload scheduled for 13:00:00 PDT Fri Apr 21 1996 (in 1 hour and 2 minutes)
Proceed with reload? [confirm]

The following example reloads the software on the router on April 20 at 2:00 a.m.:
Router# reload at 02:00 apr 20
Router# Reload scheduled for 02:00:00 PDT Sat Apr 20 1996 (in 38 hours and 9 minutes)
Proceed with reload? [confirm]
The following example cancels a pending reload:
Router# reload cancel
%Reload cancelled.

Outlook: Problems Syncing Offline Folders

From: MS KB 842284

How to create a new .ost file and synchronize the folders

To create a new .ost file, rename the old .ost file, and then synchronize the new .ost file with the computer that is running Microsoft Exchange Server. When you rename the old .ost file, Outlook creates a new file. To do this, follow these steps:

1. Quit all programs.
2. Click Start, point to Search, and then click For Files or Folders.
3. In the search dialog box, click All files and folders.
4. In the All or part of the file name tab, type *.ost .
5. Do not type anything in the A word or phrase in the file box.
6. Click the hard disk in the Look in list. Then, under the More advanced options option, click to select the Include subfolders check box, and then click Search

In the Name column, you see the .ost file. The default location for the .ost file is as follows.

For Microsoft Windows 95 and Microsoft Windows 98:
C:\Windows\Local Settings\Application Data\Microsoft\Outlook

For Microsoft Windows 2000, Microsoft Windows NT and Microsoft Windows XP:
C:\Documents and Settings\user name\Local Settings\Application Data\Microsoft\Outlook

7. Right-click the .ost file, and then click Rename. Rename the file by using a different file name extension, such as an .old file name extension instead of the .ost file name extension.
8. On the File menu, click Close.
9. Start Outlook, point to Send/receive on the Tools menu, and then click Send/Receive All.
You see the status of the new synchronization in the lower-right part of the screen, and you now have a new .ost file.

Because the .ost file is a replication of the information that is stored in the Exchange Server mailbox, this procedure does not damage any information.

Hey, Scripting Guy! How Can I Delete All the .BAK Files in a Folder That Are More Than 7 Days Old?:
"dtmDate = Date - 7

strDay = Day(dtmDate)

If Len(strDay) < 2 Then
strDay = '0' & strDay
End If

strMonth = Month(dtmDate)

If Len(strMonth) < 2 Then
strMonth = '0' & strMonth
End If

strYear = Year(dtmDate)

strTargetDate = strYear & strMonth & strDay

strComputer = '.'

Set objWMIService = GetObject('winmgmts:\\' & strComputer & '\root\cimv2')

Set FileList = objWMIService.ExecQuery _
('ASSOCIATORS OF {Win32_Directory.Name='C:\Scripts'} Where ' _
& 'ResultClass = CIM_DataFile')

For Each objFile In FileList
strDate = Left(objFile.CreationDate, 8)
If strDate < strTargetDate Then
If objFile.Extension = 'bak' Then
objFile.Delete
End If
End If
Next"