These two have now chalked up 32 draws this season (17 for Ipswich and 15 for Bristol City) including both meetings this term, with the match at Ashton Gate also ending goalless.
This was far from a dull affair though with Ipswich making the better start as David Norris shot over, then saw a dangerous cross scrambled away while Gerken did well to parry away a firm low David Healy drive.
City started to look more threatening and Brian Murphy saved efforts from Cole Skuse and former Town winger Danny Haynes. Paul Hartley fired a free-kick over and then sent in a corner which an unmarked Lewin Nyatanga headed narrowly wide.
Town threatened when Colback took a free-kick short to Grant Leadbitter whose fierce shot was parried by Gerken and then rebounded back into the keeper's arms off Daryl Murphy.
Brian Murphy saved from a Hartley long-range effort, Louis Carey saw a deflected volley fly wide and Iwelumo volleyed wide from a Hartley corner, but the best chance of the half saw loanee Iwelumo race onto Liam Fontaine's chipped pass and crash a close-range header against the bar.
Ipswich came out more fired up after the break and Daryl Murphy got a touch over the bar from Liam Rosenior's cross before a dithering Bradley Orr was robbed by Jon Walters but Gerken raced out to block him.
Gerken saved from Walters again but could only watch as Colback latched onto Leadbitter's delightful throughball and flicked his shot past the goalkeeper, but it hit the inside of the post and went back to a grateful Gerken.
Bristol City's one real threat of the second half came shortly after when Iwelumo flicked on a long ball and David Clarkson crashed in a fierce angled volley which Brian Murphy palmed away.
Gerken made another fine save to deny Daryl Murphy and then blocked Healy's follow-up, but both sides then made two changes with Town sending on two new frontmen in Pablo Counago and Connor Wickham while City replaced Lee Johnson and Hartley with Gavin Williams and Jamal Campbell-Ryce.
Gerken excelled again when he palmed away a Gareth McAuley header from Carlos Edwards' pinpoint cross before Edwards and Walters exchanged a one-two before the latter sent in a deflected 25-yarder which Gerken tipped away once more.
Counago's shot on the turn from Wickham's pass was saved and the pair linked up again when Counago laid off Rosenior's cross to Wickham and his partially blocked shot looked to be spinning into the net before Gerken plunged to save it.
McAuley put a free header over from sub Owen Garvan's cross and Garvan himself shot wide from Counago's pass while Town did have the ball in the net in stoppage time but ref Nigel Miller ruled Wickham's long throw had gone straight in after the excellent Gerken made a rare error in misjudging the ball's flight.
The final whistle brought boos of frustration from the home fans who had once again seen their side dominate without taking all three points, and this result leaves Town just four points above the drop-zone.