One of the most important pieces of equipment in any home or office network is the router. This device is responsible for connecting all of your devices to the internet and ensuring that they can communicate with each other. But did you know that the router can also be used to bootstrap your iOS devices? In this blog post, we will explore where the router bootstrap look for he iOS and how you can use this feature to your advantage. We will also discuss some of the benefits and drawbacks of using a bootstrapped iOS device.
The Default Location
When a router is powered on, it will look for the IOS in a few different places. The first place it will look is in flash memory. If the IOS is not in flash memory, the router will look for it in ROM. If the IOS is not in ROM, the router will try to load it from a TFTP server.
The Alternate Location
If the router cannot find a valid IOS image in flash memory, it will look for a valid image on TFTP server. To configure the router to boot from an alternate location, use the boot system command in global configuration mode. For example, the following commands tell the router to first look for a valid image in flash memory and if not found, to then look for a valid image on 188.8.131.52:
Router(config)#boot system flash c2800nm-advipservicesk9-mz.124-15.T7.bin
Router(config)#boot system tftp 184.108.40.206 c2800nm-advipservicesk9-mz.124-15.T7
The TFTP Server
The Trivial File Transfer Protocol (TFTP) is a simple lockstep File Transfer Protocol which allows a client to get or put a file onto a remote host. It is typically used in small deployments where there is no need for a more sophisticated file transfer protocol such as FTP. TFTP uses UDP port 69.
There are two types of TFTP:
- The first type is where the client initiates the transfer and the server sends the requested file. The client can also specify whether it wants the file to be transferred in ASCII mode or binary mode. This type of TFTP is sometimes called “push” TFTP.
- The second type of TFTP is where the server initiates the transfer and the client sends the requested file. This type of TFTP is called “pull” TFTP.
TFTP has been widely used for software distribution, firmware upgrades, and loading boot images (e.g., operating system images) onto diskless workstations, routers, firewalls, and other network devices.
The bootstrap process for a router
When a router first powers on, it will go through a process known as bootstrap in order to find and load the correct IOS image. The bootstrap process can be divided into four distinct phases:
- POST (Power-On Self-Test): In this phase, the router performs a number of hardware checks to ensure all components are functioning properly.
- BootROM: Once the POST is complete, the router will look for its BootROM code in ROM. This code is responsible for loading the IOS image from flash memory.
- Minimal IOS: If the BootROM code is unable to find a valid IOS image in flash memory, it will load a minimal version of IOS from ROM known as ROMmon (ROM monitor). ROMmon contains a limited set of commands that can be used to troubleshoot problems with the router.
- TFTP: If theBootROM code is unable to find a valid IOS image in flash memory, and there is no TFTP server configured, the router will enter setup mode. Setup mode allows you to manually configure basic settings such as IP addresses, passwords, etc.
The different types of information a router needs in order to bootstrap
A router needs different types of information in order to bootstrap. This information includes the address of the next-hop router, the address of the default gateway, the address of a DNS server, and the subnet mask. The router will also need information about the network it is connected to, including the network’s IP address and netmask.
What happens if the router can’t find the correct information?
If the router can’t find the correct information, it will boot from the next available source. This could be a TFTP server, an FTP server, or even the ROM.
How to make sure your router is bootstrapping correctly?
If your router is not bootstrapping correctly, there are a few things you can do to troubleshoot the issue.
First, check that the router is receiving power and that all cables are properly connected. If the router is still not powering on, you may need to reset the power supply.
Once the router is powered on, check the status of the bootstrap process by looking at the LED indicators. If the indicators are not lit or are flashing, this could indicate an issue with the bootstrap process.
If you believe the router is not bootstrapping correctly, you can try manually initiating the bootstrap process by issuing the “boot” command from privileged mode. This will instruct the router to look for a valid He IOS image in flash memory and load it if one is found.
If you still cannot get the router to bootstrap correctly, you may need to contact Cisco support for further assistance.
The router will look for the IOS in a few different places, depending on how it is configured. The most common place for the IOS to be located is in flash memory, but it can also be stored on a TFTP server or in NVRAM. If the router cannot find the IOS in any of these locations, it will boot from ROM instead.