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Cisco Router Secuirty

Cisco Routers are cool but i have been finding a few issues with DDOS attacks of late. Mainly DNS and NTP.

DNS DDOS

access-list 153 remark Block DOS DNS
access-list 153 permit ip host 202.62.147.50 any – Replace this with the DNS server your using
access-list 153 deny tcp any any eq domain
access-list 153 deny udp any any eq domain
access-list 153 permit ip any any

Then add

!
interface Dialer0 – your dialer interface
ip access-group 153 in

 

NTP DDOS

 

! Core NTP configuration
ntp update-calendar             ! update hardware clock (certain hardware only, i.e. 6509s)
ntp server 192.0.2.1            ! a time server you sync with
ntp peer   192.0.2.2            ! a time server you sync with and allow to sync to you
ntp source Loopback0            ! we recommend using a loopback interface for sending NTP messages if possible
!
! NTP access control
ntp access-group query-only 1   ! deny all NTP control queries
ntp access-group serve 1        ! deny all NTP time and control queries by default
ntp access-group peer 10        ! permit time sync to configured peer(s)/server(s) only
ntp access-group serve-only 20  ! permit NTP time sync requests from a select set of clients
!
! access control lists (ACLs)
access-list 1 remark utility ACL to block everything
access-list 1 deny any
!
access-list 10 remark NTP peers/servers we sync to/with
access-list 10 permit 192.0.2.1
access-list 10 permit 192.0.2.2
access-list 10 deny any
!
access-list 20 remark Hosts/Networks we allow to get time from us
access-list 20 permit 192.0.2.0 0.0.0.255
access-list 20 deny any

Taken from http://www.team-cymru.org/secure-ntp-template.html


                            

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